/* 伯特 · 褪色：墨线是几何骨架（第一性质），水彩是颜色（第二性质）。
   从哥白尼读到牛顿，水彩一层层退场；伽利略一问做完，整页褪成灰色；读到伯特晚年，颜色回来。 */
.c-burtt {
  --bg: #f3eee3; --paper: #fbf8f1; --ink: #211e1a; --ink-2: #48423a; --ink-3: #6b6358; --rule: rgba(33, 30, 26, .18);
  --acc: #2f55a0; --acc-ink: #fbf8f1;
  --head: "Noto Serif SC", "Songti SC", "STSong", serif; --body: "Noto Serif SC", "Songti SC", "STSong", serif;
  --goudy: "Sorts Mill Goudy", "Noto Serif SC", Georgia, serif;
  --bar-bg: rgba(243, 238, 227, .9); --chip-bg: rgba(251, 248, 241, .86); --chip-ring: #fbf8f1;
  --pg: #f3eee3;
  /* 颜料（rgb 三元组，方便调透明度） */
  --c-earth: 185 131 82; --c-blue: 63 98 173; --c-gold: 217 162 58; --c-red: 207 83 56; --c-gray: 150 148 143;
  --c-saffron: 224 138 42; --c-green: 111 154 75; --c-ink: 58 53 46;
}
body.c-burtt { background: var(--pg); transition: background-color 1.4s ease; }
body.c-burtt[data-cur="kepler"] { --pg: #f5eedc; }
body.c-burtt[data-cur="galileo"] { --pg: #f0ede6; }
body.c-burtt[data-cur="newton"] { --pg: #e3e3e0; }
body.c-burtt[data-cur="religion"] { --pg: #f7ecd9; }
.c-burtt main > section { background-color: var(--pg); transition: background-color 1.4s ease, filter 1.8s ease; }
/* 伽利略一问做完：前面几屏都褪成灰色（伽利略那一屏自己已经是灰的，牛顿一屏本来就是灰的） */
body.bt-drained main > section:not(#newton):not(#religion):not(#end), body.bt-drained .c3bar__prog { filter: saturate(0); }
body.bt-drained .bt-wash { opacity: 0 !important; }
.c-burtt .dlg { --dlg-bg: #efe9dc; --dlg-paper: #fcfaf5; --dlg-ink: #211e1a; --dlg-ink-2: #4f483f; --dlg-ink-3: #756d61;
  --dlg-me: #2f4c88; --dlg-me-ink: #fbf8f1; --dlg-acc: #b9472c; }
.c-burtt .c3bar { background: var(--bar-bg); background: color-mix(in srgb, var(--pg) 90%, transparent); border-bottom-color: var(--rule); transition: background-color 1.4s ease; }
.c-burtt .c3bar__prog { background: linear-gradient(90deg, rgb(var(--c-blue)), rgb(var(--c-gold)) 35%, rgb(var(--c-red)) 55%, rgb(var(--c-gray)) 72%, rgb(var(--c-saffron)) 90%); }
.c-burtt .mk { font-size: 12px; letter-spacing: .14em; color: var(--ink-3); }

/* ---------- 水彩色块 ---------- */
.bt-sw { --rgb: var(--c-earth); position: relative; display: inline-grid; place-items: center; min-width: 58px; height: 36px; padding: 0 10px;
  border-radius: 46% 54% 41% 59% / 58% 44% 56% 42%;
  background: radial-gradient(ellipse 70% 80% at 32% 40%, rgb(var(--rgb) / .42), rgb(var(--rgb) / .3) 62%, rgb(var(--rgb) / .5) 92%, rgb(var(--rgb) / .2) 100%);
  box-shadow: inset 0 0 0 1px rgb(var(--rgb) / .3), inset 0 0 9px rgb(var(--rgb) / .22);
  color: var(--ink); transition: filter 1.6s ease; }
.bt-sw b { font-family: var(--goudy); font-weight: 400; font-size: 19px; line-height: 1; letter-spacing: .02em; }
.bt-sw--earth { --rgb: var(--c-earth); }
.bt-sw--blue { --rgb: var(--c-blue); }
.bt-sw--gold { --rgb: var(--c-gold); }
.bt-sw--red { --rgb: var(--c-red);
  background: radial-gradient(ellipse 70% 80% at 30% 40%, rgb(var(--c-red) / .44), rgb(var(--c-red) / .3) 55%, transparent 80%),
    linear-gradient(100deg, transparent 48%, rgb(var(--c-gray) / .42) 64%, rgb(var(--c-gray) / .5) 100%); }
.bt-sw--gray { --rgb: var(--c-gray); }
.bt-sw--saffron { --rgb: var(--c-saffron); }
.bt-sw--ink { --rgb: var(--c-ink); }
.bt-sw--all { background: radial-gradient(circle at 18% 50%, rgb(var(--c-blue) / .45), transparent 30%), radial-gradient(circle at 40% 45%, rgb(var(--c-gold) / .5), transparent 30%),
  radial-gradient(circle at 60% 55%, rgb(var(--c-red) / .45), transparent 30%), radial-gradient(circle at 80% 48%, rgb(var(--c-gray) / .45), transparent 28%),
  radial-gradient(circle at 96% 52%, rgb(var(--c-saffron) / .5), transparent 24%); box-shadow: none; }
.bt-sw--big { min-width: 96px; height: 52px; padding: 0 14px; }
.bt-sw--big b { font-size: 31px; }
.bt-sw--strip { display: block; width: 100%; height: 14px; min-width: 0; border-radius: 40% 60% 55% 45% / 60% 40% 60% 40%; }

/* ---------- 按钮与说明 ---------- */
.bt-cap-k { margin: 0 0 12px; display: flex; flex-wrap: wrap; align-items: baseline; gap: 4px 10px; font-size: 13.5px; line-height: 1.6; color: var(--ink-2); }
.bt-cap-k span { padding: 1px 8px; border: 1px solid var(--ink); font-size: 12px; letter-spacing: .1em; color: var(--ink); background: var(--paper); }
.bt-ctl { display: flex; flex-wrap: wrap; align-items: center; gap: 8px; margin: 14px 0 0; }
.bt-ctl__lab { margin-right: 2px; font-size: 13px; letter-spacing: .12em; color: var(--ink-3); }
.bt-btn { display: inline-flex; align-items: center; justify-content: center; gap: 6px; min-height: 42px; padding: 7px 14px; border: 1.5px solid var(--ink);
  border-radius: 3px; background: var(--paper); color: var(--ink); font: 500 14.5px/1.3 var(--body); cursor: pointer; transition: background-color .25s, color .25s, box-shadow .25s; }
.bt-btn:hover { box-shadow: 3px 3px 0 rgb(var(--c-ink) / .18); }
.bt-btn[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
.bt-btn--main { background: var(--acc); border-color: var(--acc); color: var(--acc-ink); }
.bt-btn--main[aria-pressed="true"] { background: var(--paper); color: var(--acc); }
.bt-btn--ghost { border-style: dashed; background: transparent; }
.bt-hint { font-size: 13px; color: var(--ink-3); }
.bt-notes { margin: 14px 0 0; min-height: 5.6em; padding: 12px 14px; border-left: 3px solid rgb(var(--rgb, var(--c-blue))); background: rgb(251 248 241 / .72);
  font-size: 15px; line-height: 1.8; color: var(--ink-2); }
.bt-notes p { margin: 0; }
.bt-notes p + p { margin-top: 8px; }
.js .bt-notes > [data-s]:not(.is-on) { display: none; }
.js .bt-notes > .is-on { animation: bt-in .5s ease both; }
@keyframes bt-in { from { opacity: 0; transform: translateY(4px); } to { opacity: 1; transform: none; } }

/* ---------- 首屏 ---------- */
.c-burtt .c3hero { padding: calc(var(--bar) + 22px) clamp(16px, 4.5vw, 72px) 46px; }
.bt-hero { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1.12fr) 214px; grid-template-areas: "txt plate qs"; gap: 18px clamp(22px, 3vw, 44px);
  max-width: 1320px; margin: 0 auto; align-items: center; }
.bt-hero__txt { grid-area: txt; position: relative; isolation: isolate; }
.bt-k { margin: 0; font-size: 13px; letter-spacing: .16em; color: rgb(var(--c-blue)); }
.bt-name { position: relative; margin: 2px 0 0; font-family: var(--head); font-weight: 900; font-size: clamp(76px, 10vw, 148px); line-height: 1.02; letter-spacing: .08em; }
.bt-name::before { content: ""; position: absolute; z-index: -1; left: -.12em; top: .06em; width: 2.6em; height: 1.02em; border-radius: 52% 48% 44% 56% / 60% 50% 50% 40%;
  background: radial-gradient(ellipse 60% 70% at 28% 45%, rgb(var(--c-blue) / .26), transparent 70%), radial-gradient(ellipse 50% 60% at 70% 62%, rgb(var(--c-gold) / .3), transparent 70%);
  transition: opacity 1.6s ease; }
body.bt-drained .bt-name::before { opacity: 0; }
.bt-en { margin: 6px 0 18px; display: flex; flex-wrap: wrap; align-items: baseline; gap: 4px 16px; font-family: var(--goudy); font-size: 25px; font-style: italic; color: var(--ink); }
.bt-yr { font-style: normal; font-size: 21px; color: var(--ink-3); letter-spacing: .04em; }
.bt-who { margin: 0 0 4px; font-size: 19px; font-weight: 600; line-height: 1.55; }
.bt-now { margin: 0 0 16px; font-size: 14.5px; color: var(--ink-2); }
.bt-rel { margin: 0 0 14px; padding: 12px 16px; background: rgb(var(--c-blue) / .07); border-left: 3px solid rgb(var(--c-blue) / .7); }
.bt-rel .mk { margin: 0 0 4px; color: rgb(var(--c-blue)); }
.bt-rel p:last-child { margin: 0; font-size: 15px; line-height: 1.8; }
.bt-mainbooks { margin: 0 0 14px; font-size: 15px; line-height: 1.8; }
.bt-mainbooks .mk { display: inline; margin: 0 10px 0 0; }
.bt-nw { white-space: nowrap; }
.bt-mainbooks small { margin-left: 3px; font-family: var(--goudy); font-size: 15px; color: var(--ink-3); }
.bt-go { margin: 0; }
.c-burtt .c3-btn { border-radius: 3px; font-family: var(--body); min-height: 42px; }
.c-burtt .c3-btn--go { background: var(--acc); border-color: var(--acc); color: var(--acc-ink); }
.c-burtt .c3-btn--deep { background: transparent; color: var(--ink); border: 1.5px solid var(--ink); }

.bt-plate { grid-area: plate; margin: 0; }
.bt-plate__img { position: relative; width: min(100%, calc((100svh - var(--bar) - 150px) * .8765)); min-width: min(100%, 280px); margin: 0 auto; }
.bt-plate__ink { display: block; width: 100%; height: auto; mix-blend-mode: multiply; }
.bt-plate__wash { position: absolute; inset: 0; width: 100%; height: 100%; mix-blend-mode: multiply; opacity: var(--wash, 1); transition: opacity 1.8s ease; animation: bt-paint 2.6s .2s ease-out backwards; }
@keyframes bt-paint { from { opacity: 0; } }
.bt-plate figcaption { max-width: 560px; margin: 8px auto 0; font-size: 13px; line-height: 1.7; color: var(--ink-2); }

/* 问题目录：像图版右边的图例 */
.bt-qs { grid-area: qs; align-self: center; padding-left: 16px; border-left: 1px solid var(--rule); }
.bt-qs .mk { margin-bottom: 10px; }
.bt-qs ol { list-style: none; margin: 0; padding: 0; display: flex; flex-direction: column; gap: 8px; }
.bt-qs a { display: grid; grid-template-columns: 60px minmax(0, 1fr); align-items: center; gap: 10px; min-height: 44px; text-decoration: none; }
.bt-qs .bt-sw { min-width: 0; width: 60px; height: 32px; padding: 0; }
.bt-qs .bt-sw b { font-size: 17px; }
.bt-qs a span:last-child { font-size: 14.5px; line-height: 1.5; font-weight: 600; }
.bt-qs a:hover span:last-child, .bt-qs a:focus-visible span:last-child { text-decoration: underline; text-underline-offset: 3px; }

.bt-band { max-width: 1320px; margin: 40px auto 0; padding-top: 22px; border-top: 1px solid var(--rule);
  display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr) minmax(0, 1.25fr) minmax(0, .9fr); gap: 28px; }
.bt-band__c .mk { margin-bottom: 8px; }
.c-burtt .c3-feats { margin: 0; padding: 0; list-style: none; counter-reset: f; }
.c-burtt .c3-feats li { counter-increment: f; position: relative; padding: 5px 0 5px 28px; font-size: 14.5px; line-height: 1.65; border-bottom: 1px solid var(--rule); }
.c-burtt .c3-feats li::before { content: counter(f); position: absolute; left: 0; top: 4px; font-family: var(--goudy); font-size: 18px; color: rgb(var(--c-blue)); }
.bt-facts { margin: 0; font-size: 14.5px; line-height: 1.85; color: var(--ink-2); }
.c-burtt .c3-books li, .c-burtt .c3-links li { border-bottom: 1px solid var(--rule); font-size: 14.5px; }
.c-burtt .c3-books li > a, .c-burtt .c3-links li > a, .c-burtt .c3-works li > a { display: inline-block; padding: 7px 0 5px; }
.c-burtt .c3-books small, .c-burtt .c3-links small { font-size: 12.5px; color: var(--ink-3); }

/* ---------- 每一问 ---------- */
.c-burtt .c3q { display: block; padding: 34px clamp(16px, 4.5vw, 72px) 64px; }
.bt-q { max-width: 1320px; margin: 0 auto; display: grid; grid-template-columns: minmax(0, 1.08fr) minmax(0, .92fr); grid-template-areas: "head head" "art txt";
  gap: 18px clamp(24px, 4vw, 60px); align-items: start; }
.c-burtt .c3q--2 .bt-q, .c-burtt .c3q--4 .bt-q { grid-template-columns: minmax(0, .92fr) minmax(0, 1.08fr); grid-template-areas: "head head" "txt art"; }
.bt-q__head { grid-area: head; }
.bt-q__art { grid-area: art; min-width: 0; }
.bt-q__txt { grid-area: txt; min-width: 0; }
.bt-q__when { margin: 0; display: flex; flex-wrap: wrap; align-items: center; gap: 6px 14px; font-size: 14.5px; color: var(--ink-2); }
.bt-q__n { font-size: 12.5px; letter-spacing: .14em; color: var(--ink-3); }
.c-burtt .c3q__q { margin: 8px 0 0; font-size: clamp(28px, 3.3vw, 46px); line-height: 1.22; letter-spacing: .02em; }
.c-burtt .c3q__lede { font-size: 16.5px; line-height: 1.95; text-align: justify; margin: 0 0 16px; }
.c-burtt .c3-quote { margin: 18px 0; padding: 14px 0 14px 18px; border-left: 0; position: relative; }
.c-burtt .c3-quote::before { content: ""; position: absolute; left: 0; top: 10px; bottom: 10px; width: 5px; border-radius: 3px 5px 4px 6px;
  background: linear-gradient(rgb(var(--rgb, var(--c-blue)) / .75), rgb(var(--rgb, var(--c-blue)) / .35)); }
.c-burtt .c3-quote blockquote p { font-size: 18px; line-height: 1.75; }
.c-burtt .c3-orig { font-family: var(--goudy); font-size: 15.5px; color: var(--ink-2); }
.c-burtt .c3-quote figcaption { color: var(--ink-3); }
.c-burtt .c3-tags li { border-radius: 2px; border-color: var(--rule); background: rgb(251 248 241 / .6); }
.c-burtt .c3-works li a { text-decoration-color: rgb(var(--rgb, var(--c-blue)) / .6); text-underline-offset: 3px; }
.c-burtt .c3-works small { color: var(--ink-3); }
.c-burtt .talk { border-color: var(--rule); background: var(--chip-bg); }
.c-burtt .c3-ask { border-color: rgb(var(--c-ink) / .3); }
.c-burtt .c3-ask small { color: var(--ink-3); }
.c-burtt .c3-deeplink { color: var(--ink); text-decoration-color: rgb(var(--rgb, var(--c-blue))); text-decoration-thickness: 2px; text-underline-offset: 4px; }
/* 每一问的颜料 */
.c-burtt #foundations { --rgb: var(--c-earth); }
.c-burtt #copernicus { --rgb: var(--c-blue); }
.c-burtt #kepler { --rgb: var(--c-gold); }
.c-burtt #galileo { --rgb: var(--c-red); }
.c-burtt #newton { --rgb: 70 70 68; --acc: #3d3d3b; --ink-3: #5c5b57; --ink-2: #3f3e3b; --paper: #f4f4f2; --chip-bg: rgba(244, 244, 242, .9);
  background-image: linear-gradient(rgb(0 0 0 / .045) 1px, transparent 1px), linear-gradient(90deg, rgb(0 0 0 / .045) 1px, transparent 1px); background-size: 26px 26px; }
.c-burtt #religion { --rgb: var(--c-saffron); --acc: #b9472c; }

/* ---------- 第一问：地基剖面 ---------- */
.bt-fd { --rgb: var(--c-earth); }
.bt-fd__site { position: relative; max-width: 560px; margin: 0 auto; }
.bt-fd__bldg { display: block; width: 100%; height: auto; overflow: visible; }
.bt-fd__wash { opacity: .75; transition: opacity 1.6s ease; }
.bt-fd__frieze { font: 600 17px var(--head); letter-spacing: .55em; fill: var(--ink); }
.bt-fd__pit { position: relative; padding: 8px 0 0; margin-top: -1px;
  background: repeating-linear-gradient(-45deg, rgb(var(--c-ink) / .2) 0 1px, transparent 1px 8px), linear-gradient(rgb(var(--c-earth) / .2), rgb(var(--c-earth) / .32)); }
.bt-fd__courses { list-style: none; margin: 0; padding: 0 0 0; display: flex; flex-direction: column; align-items: center; gap: 3px; }
.bt-fd__c { width: var(--w); transition: transform .6s ease, opacity .6s ease; }
.bt-fd__c button { --s: 214 196 166; width: 100%; min-height: 42px; display: flex; align-items: center; gap: 10px; padding: 6px 12px; border: 1.5px solid var(--ink);
  background: rgb(var(--s) / .92); color: var(--ink); font: 500 14.5px/1.35 var(--body); text-align: left; cursor: pointer;
  box-shadow: inset 0 -5px 8px rgb(var(--c-ink) / .08); transition: background-color .3s, box-shadow .3s, transform .3s; }
.bt-fd__c--newton button { --s: 224 216 200; }
.bt-fd__c--boyle button { --s: 221 203 172; }
.bt-fd__c--english button { --s: 216 192 156; }
.bt-fd__c--descartes button { --s: 210 182 141; }
.bt-fd__c--galileo button { --s: 204 172 128; }
.bt-fd__c--copernicus button { --s: 196 160 115; }
.bt-fd__rock button { --s: 92 86 78; color: #f6f1e6;
  background: repeating-linear-gradient(60deg, rgb(255 255 255 / .09) 0 1px, transparent 1px 6px), rgb(var(--s)); }
.bt-fd__c button:hover { transform: translateX(3px); }
.bt-fd__c button[aria-pressed="true"] { background: rgb(var(--c-gold) / .55); box-shadow: inset 0 0 0 2px var(--ink), 4px 4px 0 rgb(var(--c-ink) / .25); }
.bt-fd__rock button[aria-pressed="true"] { background: #3a352e; color: #fff; }
.bt-fd__n { min-width: 2.4em; font-family: var(--goudy); font-size: 18px; line-height: 1; color: var(--ink); }
.bt-fd__rock .bt-fd__n { color: #f2c66b; }
.bt-fd__y { margin-left: auto; padding-left: 8px; font-family: var(--goudy); font-size: 16px; color: var(--ink); white-space: nowrap; }
.bt-fd__earth { position: absolute; inset: 0 -1px -1px; display: grid; place-items: center; z-index: 2;
  background: repeating-linear-gradient(-45deg, rgb(var(--c-ink) / .5) 0 1.2px, transparent 1.2px 6px), linear-gradient(#cbb894, #b79f76);
  clip-path: inset(0 0 0 0); transition: clip-path 1.1s cubic-bezier(.6, 0, .2, 1); }
.bt-fd__dig { display: inline-flex; align-items: center; gap: 8px; min-height: 44px; padding: 6px 18px; background: var(--paper); border: 1.5px solid var(--ink); color: var(--ink);
  font: 600 15px/1.2 var(--body); letter-spacing: .2em; cursor: pointer; box-shadow: 4px 4px 0 rgb(var(--c-ink) / .25); }
.bt-fd__dig:hover { background: #fff; }
.bt-fd.is-cut .bt-fd__earth { clip-path: inset(100% 0 0 0); }
.no-js .bt-fd__earth { display: none; }
.no-js .bt-fd__ctl, .no-js .bt-fd__notes > [data-s="sec"], .no-js .bt-bal .bt-ctl, .no-js .bt-gw__ctl, .no-js .bt-nt .bt-ctl { display: none; }
.js .bt-fd:not(.is-cut) .bt-fd__c { opacity: .2; }
.bt-fd__survey { margin: 14px 0 0; font-size: 14px; line-height: 1.8; color: var(--ink-2); }
.bt-fd__survey b { margin-right: 8px; padding: 0 6px; border: 1px solid var(--ink); font-weight: 600; font-size: 12.5px; letter-spacing: .1em; }

/* ---------- 第二问：天平 ---------- */
.bt-bal { --rgb: var(--c-blue); --tilt: -8deg; }
.bt-bal[data-judge="pla"] { --tilt: 8deg; }
.bt-bal__stage { position: relative; height: 372px; max-width: 620px; margin: 0 auto; container-type: inline-size; overflow-x: clip; }
.bt-bal__post { position: absolute; left: 50%; top: 30px; bottom: 0; width: 120px; transform: translateX(-50%); pointer-events: none; }
.bt-bal__post::before { content: ""; position: absolute; left: 53px; top: 0; bottom: 18px; width: 14px; border: 1.5px solid var(--ink); border-radius: 6px 6px 0 0;
  background: repeating-linear-gradient(90deg, rgb(var(--c-ink) / .25) 0 1px, transparent 1px 4px), #d8c7a6; }
.bt-bal__post::after { content: ""; position: absolute; left: 0; right: 0; bottom: 0; height: 18px; border: 1.5px solid var(--ink); border-radius: 50% 50% 4px 4px / 80% 80% 4px 4px;
  background: repeating-linear-gradient(-45deg, rgb(var(--c-ink) / .3) 0 1px, transparent 1px 5px), #d8c7a6; }
.bt-bal__post i { position: absolute; left: 50%; top: -9px; width: 20px; height: 20px; margin-left: -10px; border: 1.5px solid var(--ink); border-radius: 50%; background: rgb(var(--c-gold)); z-index: 2; }
.bt-bal__beam { position: absolute; left: 21%; right: 21%; top: 30px; height: 7px; border: 1.5px solid var(--ink); border-radius: 4px; background: #c9b48c;
  transform: rotate(var(--tilt)); transition: transform 1.3s cubic-bezier(.34, 1.45, .5, 1); z-index: 1; }
.bt-bal__beam::before, .bt-bal__beam::after { content: ""; position: absolute; top: -6px; width: 14px; height: 14px; border: 1.5px solid var(--ink); border-radius: 50%; background: var(--paper); }
.bt-bal__beam::before { left: -8px; } .bt-bal__beam::after { right: -8px; }
.bt-bal__hang { position: absolute; top: 2px; width: 0; height: 0; transform: rotate(calc(-1 * var(--tilt))); transition: transform 1.3s cubic-bezier(.34, 1.45, .5, 1); }
.bt-bal__hang--l { left: -1px; } .bt-bal__hang--r { right: -1px; }
.bt-bal__pan { position: absolute; top: 0; left: 0; width: min(230px, 40cqw); transform: translateX(-50%); display: flex; flex-direction: column; align-items: center; }
.bt-bal__pan::before { content: ""; order: 0; width: 72%; height: 42px; margin-top: 4px;
  background: linear-gradient(to bottom right, transparent calc(50% - 1px), var(--ink) calc(50% - .4px), var(--ink) calc(50% + .4px), transparent calc(50% + 1px)) left / 50% 100% no-repeat,
    linear-gradient(to bottom left, transparent calc(50% - 1px), var(--ink) calc(50% - .4px), var(--ink) calc(50% + .4px), transparent calc(50% + 1px)) right / 50% 100% no-repeat; }
.bt-bal__who { order: 3; margin: 0; width: 100%; padding: 4px 0 2px; border: 1.5px solid var(--ink); border-top: 0; border-radius: 0 0 50% 50% / 0 0 100% 100%;
  text-align: center; font-weight: 900; font-size: 15px; letter-spacing: .3em; }
.bt-bal__pan--p .bt-bal__who { background: rgb(var(--c-earth) / .3); }
.bt-bal__pan--c .bt-bal__who { background: rgb(var(--c-gold) / .38); }
.bt-bal__pan ul { order: 2; list-style: none; margin: 0; padding: 0; width: 100%; display: flex; flex-direction: column-reverse; gap: 3px; border-bottom: 1.5px solid var(--ink); }
.bt-bal__pan li { padding: 3px 8px; border: 1px solid var(--ink); background: var(--paper); text-align: center; font-size: 13.5px; line-height: 1.35; }
.bt-bal__pan li b { font-weight: 600; }
.bt-bal__pan li small { display: block; font-size: 11.5px; color: var(--ink-2); line-height: 1.4; }
.bt-bal__pan--p li { background: rgb(var(--c-earth) / .14); }
.bt-bal__math { background: rgb(var(--c-gold) / .55) !important; padding: 7px 8px !important; transition: opacity .8s, transform .8s, background-color .8s, border-color .8s; }
.bt-bal[data-judge="emp"] .bt-bal__math { opacity: .8; border-style: dashed; background: transparent !important; transform: translateY(-16px); }
.bt-bal[data-judge="emp"] .bt-bal__math b::after { content: "不压秤"; display: block; font-weight: 400; font-size: 12px; letter-spacing: .3em; color: var(--ink-2); }
.bt-bal[data-judge="pla"] .bt-bal__math { transform: scale(1.08); box-shadow: 0 6px 0 -2px rgb(var(--c-gold) / .55); }
.js .bt-bal[data-judge="emp"] .bt-bal__math { animation: bt-float 2.6s ease-in-out infinite; }
@keyframes bt-float { 0%, 100% { translate: 0 0; } 50% { translate: 0 -5px; } }

/* ---------- 第三问：正多面体模型 ---------- */
.bt-kp { --rgb: var(--c-gold); }
.bt-kp__stage { position: relative; width: min(100%, 480px, calc(100svh - var(--bar) - 330px)); min-width: min(100%, 320px); aspect-ratio: 1; margin: 0 auto; }
.bt-kp__cv { display: block; width: 100%; height: 100%; cursor: grab; touch-action: pan-y; border-radius: 50%; outline-offset: 6px; }
.bt-kp__cv:active { cursor: grabbing; }
.bt-kp__tag { position: absolute; left: 0; top: 4px; margin: 0; padding: 2px 10px; background: var(--paper); border: 1px solid var(--ink); font-size: 13px; letter-spacing: .08em; pointer-events: none; }
.bt-kp__tag:empty { display: none; }
.bt-kp__tag i, .bt-kp__h i, .bt-kp__steps i { font-family: var(--goudy); font-style: italic; }
.bt-kp__steps { list-style: none; margin: 10px 0 0; padding: 0; display: flex; flex-wrap: wrap; justify-content: center; gap: 5px; }
.bt-kp__steps button { display: inline-flex; align-items: center; gap: 3px; min-height: 42px; min-width: 42px; padding: 4px 9px; border: 1.5px solid var(--ink); border-radius: 22px;
  background: var(--paper); color: var(--ink); font: 500 14px/1 var(--body); cursor: pointer; }
.bt-kp__steps button i { font-size: 17px; color: rgb(var(--c-blue)); }
.bt-kp__steps button[aria-pressed="true"] { background: var(--ink); color: var(--paper); }
.bt-kp__steps button[aria-pressed="true"] i { color: rgb(var(--c-gold)); }
.bt-kp__h { margin: 0 0 4px !important; font-weight: 700; color: var(--ink); }
.bt-kp__h i { margin-right: 6px; font-size: 18px; color: rgb(var(--c-gold)); }
.bt-kp__vs { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.bt-kp__vs span { padding: 8px 10px; background: rgb(var(--c-gold) / .14); }
.bt-kp__vs span + span { background: rgb(var(--c-blue) / .1); }
.bt-kp__vs b { display: block; margin-bottom: 2px; font-size: 13px; letter-spacing: .14em; }
.no-js .bt-kp__stage, .no-js .bt-kp__steps { display: none; }
.no-js .bt-kp__notes > div + div { margin-top: 12px; }

/* ---------- 第四问：第二性质退场 ---------- */
.bt-gw { --rgb: var(--c-red);
  --g-sky1: #6f98cf; --g-sky2: #f1c27c; --g-sky3: #ee9f7f; --g-sun: #f2b33d; --g-hill1: #93b78a; --g-hill2: #6f9b5e; --g-ground: #a9c47f; --g-trunk: #8a5a3b;
  --g-leaf: #5d8f4e; --g-fruit: #e0663a; --g-bird: #4f7fc4; --g-flower: #e77fa0; --g-flc: #f4d35e; --g-coat: #b5523b; }
.bt-gw.is-nocolor { --g-sky1: #b4b4b2; --g-sky2: #dcdcda; --g-sky3: #d0d0ce; --g-sun: #d9d9d7; --g-hill1: #b8b8b6; --g-hill2: #9e9e9c; --g-ground: #c3c3c1;
  --g-trunk: #8c8c8a; --g-leaf: #8f8f8d; --g-fruit: #9b9b99; --g-bird: #8d8d8b; --g-flower: #b1b1af; --g-flc: #d8d8d6; --g-coat: #8a8a88; }
.bt-gw__stage { position: relative; }
.bt-gw__svg { display: block; width: 100%; height: auto; overflow: visible; font-family: var(--body); }
.bt-gw .g-sky1 { stop-color: var(--g-sky1); } .bt-gw .g-sky2 { stop-color: var(--g-sky2); } .bt-gw .g-sky3 { stop-color: var(--g-sky3); }
.bt-gw stop, .bt-gw__paint *, .bt-gw .p-coat { transition: stop-color 1.6s ease, fill 1.6s ease; }
.bt-gw .p-sun { fill: var(--g-sun); } .bt-gw .p-hill1 { fill: var(--g-hill1); } .bt-gw .p-hill2 { fill: var(--g-hill2); } .bt-gw .p-ground { fill: var(--g-ground); }
.bt-gw .p-trunk { fill: var(--g-trunk); } .bt-gw .p-leaf { fill: var(--g-leaf); opacity: .92; } .bt-gw .p-fruit { fill: var(--g-fruit); } .bt-gw .p-bird { fill: var(--g-bird); }
.bt-gw .p-flower { fill: var(--g-flower); } .bt-gw .p-flc { fill: var(--g-flc); } .bt-gw .p-coat { fill: var(--g-coat); }
.bt-gw__paint { opacity: .9; }
.bt-gw__song { fill: #2f4c88; stroke: #2f4c88; font-size: 22px; transition: opacity 1s ease, transform 1s ease; }
.bt-gw__scent { stroke: #b0679a; transition: opacity 1s ease; }
.bt-gw__juice { fill: #e0663a; transition: opacity 1s ease, fill 1.6s ease; }
.bt-gw.is-nocolor .bt-gw__juice { fill: #9b9b99; }
.bt-gw.is-nocolor .bt-gw__song { fill: #555; stroke: #555; }
.bt-gw.is-nocolor .bt-gw__scent { stroke: #888; }
.bt-gw.is-nosound .bt-gw__song, .bt-gw.is-nosmell .bt-gw__scent, .bt-gw.is-notaste .bt-gw__juice { opacity: 0; }
.bt-gw__geo { opacity: 0; transition: opacity 1.2s ease .5s; }
.bt-gw.is-all .bt-gw__geo { opacity: 1; }
.bt-gw.is-all .bt-gw__paint { opacity: .45; }
.bt-gw__lab { font: italic 17px var(--goudy); }
.bt-gw__man { transform: translate(470px, 300px); transition: transform 2s cubic-bezier(.5, 0, .3, 1) .6s; }
.bt-gw.is-all .bt-gw__man { transform: translate(594px, 300px); }
.bt-gw__mind circle { transform-box: fill-box; transform-origin: center; transform: scale(0); transition: transform .6s cubic-bezier(.3, 1.6, .5, 1) .9s; }
.bt-gw .m-color { fill: #e0663a; } .bt-gw .m-sound { fill: #2f4c88; } .bt-gw .m-smell { fill: #c76d9a; } .bt-gw .m-taste { fill: #e0a83a; }
.bt-gw.is-nocolor .m-color, .bt-gw.is-nosound .m-sound, .bt-gw.is-nosmell .m-smell, .bt-gw.is-notaste .m-taste { transform: scale(1); }
.bt-gw__spec { font: 600 15px var(--body); letter-spacing: .3em; fill: var(--ink); opacity: 0; transition: opacity .8s ease 2.2s; }
.bt-gw.is-all .bt-gw__spec { opacity: 1; }
.bt-gw__fly { font: 700 22px var(--head); transform-box: fill-box; transform-origin: center; pointer-events: none; }
.bt-gw__fly--color { fill: #e0663a; } .bt-gw__fly--sound { fill: #2f4c88; } .bt-gw__fly--smell { fill: #c76d9a; } .bt-gw__fly--taste { fill: #d39a2a; }
.bt-gw__q { flex-direction: column; gap: 0; min-width: 64px; line-height: 1.2; }
.bt-gw__q small { font-size: 11px; letter-spacing: .2em; opacity: .78; }
.bt-gw__q[aria-pressed="true"] small { opacity: 1; }
.bt-gw__q[aria-pressed="true"] span { text-decoration: line-through; text-decoration-thickness: 1.5px; }
.bt-fig { margin: 18px 0 0; display: grid; grid-template-columns: 150px minmax(0, 1fr); gap: 14px; align-items: end; }
.bt-fig img { display: block; width: 100%; height: auto; mix-blend-mode: multiply; }
.bt-fig figcaption { font-size: 13px; line-height: 1.7; color: var(--ink-2); }

/* ---------- 第五问：灰色的一页 ---------- */
.bt-nt { --rgb: 70 70 68; }
.bt-nt__page { position: relative; max-width: 560px; margin: 0 auto; background: #f4f4f2; box-shadow: 0 1px 0 rgb(0 0 0 / .08), 8px 10px 0 rgb(0 0 0 / .06); }
.bt-nt__page img { display: block; width: 100%; height: auto; mix-blend-mode: multiply; transition: opacity .9s ease, filter .9s ease; }
.bt-nt__hl { position: absolute; display: block; pointer-events: none; border-bottom: 2.5px solid #161616; background: rgb(0 0 0 / .07); opacity: 0; transition: opacity .5s ease; }
.bt-nt__hl--a { left: 29.5%; width: 67.5%; top: 49.2%; height: 4.3%; }
.bt-nt__hl--b { left: 14.5%; width: 82.5%; top: 53.8%; height: 4.3%; }
.bt-nt__hl--c { left: 14.5%; width: 83%; top: 58.5%; height: 4.3%; }
.bt-nt__hl--d { left: 14.5%; width: 83%; top: 63.1%; height: 4.3%; }
.bt-nt__hl--e { left: 14.5%; width: 83%; top: 67.6%; height: 4.3%; }
.bt-nt__hl--f { left: 14.5%; width: 23%; top: 72.1%; height: 4.3%; }
.bt-nt__hl--g { left: 88.6%; width: 8.6%; top: 53.4%; height: 5.2%; border: 2.5px solid #161616; border-radius: 50%; background: transparent; transform: rotate(-3deg) scale(1.22); }
.bt-nt[data-r="pos"] .bt-nt__hl:not(.bt-nt__hl--g) { opacity: 1; }
.bt-nt[data-r="koyre"] .bt-nt__hl--g { opacity: 1; }
.bt-nt[data-r="cassirer"] .bt-nt__page img { opacity: .55; }
.bt-nt[data-r="burtt"] .bt-nt__page img { opacity: .07; filter: blur(1px); }
.bt-nt__scrawl { position: absolute; left: 6%; right: 6%; top: 36%; margin: 0; text-align: center; font: 600 clamp(18px, 2.2vw, 25px)/1.7 var(--head); color: #161616;
  opacity: 0; transform: rotate(-2deg) translateY(8px); transition: opacity .9s ease .3s, transform .9s ease .3s; pointer-events: none; }
.bt-nt[data-r="burtt"] .bt-nt__scrawl { opacity: 1; transform: rotate(-2deg); }
.no-js .bt-nt__scrawl { display: none; }
.bt-nt__notes b { margin-right: 8px; padding: 0 6px; border: 1px solid currentColor; font-size: 12.5px; letter-spacing: .1em; color: var(--ink); }

/* ---------- 第六问：颜色回来 ---------- */
.bt-rl { --rgb: var(--c-saffron); }
.bt-rl__leaf { margin: 0; }
.bt-rl__img { position: relative; overflow: hidden; border-radius: 2px; box-shadow: 0 10px 30px -14px rgb(120 60 20 / .45); }
.bt-rl__img img { display: block; width: 100%; height: auto; }
.js .bt-rl__img img { filter: grayscale(1) contrast(.92) brightness(1.05); transition: filter 3.2s ease .2s; }
.js .bt-rl.is-bloom .bt-rl__img img { filter: none; }
.bt-rl__leaf figcaption { margin-top: 8px; font-size: 13px; line-height: 1.7; color: var(--ink-2); }
.bt-rl__toc { margin-top: 18px; }
.bt-rl__toc ol { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 7px 10px; }
.bt-rl__toc li { --leaf: 224 196 140; position: relative; display: flex; align-items: center; min-height: 40px; padding: 6px 12px 6px 26px; border-radius: 999px / 46%;
  border: 1px solid rgb(var(--c-ink) / .35); font-size: 14px; line-height: 1.35;
  background: linear-gradient(180deg, rgb(255 255 255 / .35), transparent 45%), rgb(var(--leaf) / .9); }
.bt-rl__toc li::before { content: ""; position: absolute; left: 10px; top: 50%; width: 8px; height: 8px; margin-top: -4px; border-radius: 50%; background: rgb(var(--dot, 200 69 47)); }
.bt-rl__toc li:nth-child(3n+2) { --dot: 138 163 124; } .bt-rl__toc li:nth-child(3n) { --dot: 224 168 58; }
.js .bt-rl__toc li { background: #dcdad6; transition: background-color 1s ease, background 1s ease; transition-delay: calc(.5s + var(--i) * .22s); }
.js .bt-rl__toc li::before { background: #9a9893; transition: background-color 1s ease; transition-delay: calc(.6s + var(--i) * .22s); }
.js .bt-rl.is-bloom .bt-rl__toc li { background: linear-gradient(180deg, rgb(255 255 255 / .35), transparent 45%), rgb(var(--leaf) / .9); }
.js .bt-rl.is-bloom .bt-rl__toc li::before { background: rgb(var(--dot, 200 69 47)); }
.bt-rl__n { margin: 10px 0 0; font-size: 13.5px; line-height: 1.75; color: var(--ink-2); }

/* ---------- 结尾 ---------- */
.bt-end { max-width: 1100px; margin: 0 auto; }
.bt-end__k { margin: 0 0 16px; }
.c-burtt .c3end h2 { font-weight: 900; letter-spacing: .04em; }
.c-burtt .c3-lin li { border-radius: 2px; border-color: var(--rule); background: rgb(251 248 241 / .78); }

/* ---------- 侧边目录：色票 ---------- */
.c-burtt .c3toc a { color: var(--ink-3); font-size: 12.5px; }
.c-burtt .c3toc a b { font-family: var(--goudy); font-size: 14px; }
.c-burtt .c3toc a::after { --rgb: var(--c-earth); width: 15px; height: 11px; border: 0; border-radius: 46% 54% 41% 59% / 58% 44% 56% 42%;
  background: rgb(var(--rgb) / .55); box-shadow: inset 0 0 0 1px rgb(var(--rgb) / .45); transition: width .3s, height .3s, filter 1.6s; }
.c-burtt .c3toc .bt-t--blue::after { --rgb: var(--c-blue); }
.c-burtt .c3toc .bt-t--gold::after { --rgb: var(--c-gold); }
.c-burtt .c3toc .bt-t--red::after { --rgb: var(--c-red); }
.c-burtt .c3toc .bt-t--gray::after { --rgb: var(--c-gray); }
.c-burtt .c3toc .bt-t--saffron::after { --rgb: var(--c-saffron); }
.c-burtt .c3toc .bt-t--ink::after { --rgb: var(--c-ink); }
.c-burtt .c3toc .bt-t--all::after { background: linear-gradient(90deg, rgb(var(--c-blue) / .6), rgb(var(--c-gold) / .6), rgb(var(--c-red) / .6)); box-shadow: none; }
.c-burtt .c3toc a[aria-current="true"] { color: var(--ink); }
.c-burtt .c3toc a[aria-current="true"]::after { width: 24px; height: 15px; background: rgb(var(--rgb) / .85); }
.c-burtt .c3toc a.bt-t--all[aria-current="true"]::after { background: linear-gradient(90deg, rgb(var(--c-blue) / .8), rgb(var(--c-gold) / .8), rgb(var(--c-red) / .8)); }
body.bt-drained .c3toc a:not(.bt-t--saffron):not(.bt-t--ink)::after { filter: saturate(0); }

/* ---------- 响应式 ---------- */
@media (min-width: 861px) {
  .c-burtt .c3hero, .c-burtt .c3q, .c-burtt .c3end { padding-right: max(clamp(16px, 4.5vw, 72px), 52px); }
}
@media (min-width: 1301px) {
  .c-burtt .c3hero, .c-burtt .c3q, .c-burtt .c3end { padding-right: 104px; }
}
@media (max-width: 1279px) and (min-width: 961px) {
  .bt-hero { grid-template-columns: minmax(0, 1fr) minmax(300px, .82fr); grid-template-areas: "txt plate" "txt qs"; align-items: start; }
  .bt-hero__txt { align-self: center; }
  .bt-plate__img { width: min(100%, calc((100svh - var(--bar) - 380px) * .8765)); }
  .bt-qs { align-self: start; padding: 12px 0 0; border-left: 0; border-top: 1px solid var(--rule); }
  .bt-qs .mk { margin-bottom: 4px; }
  .bt-qs ol { gap: 2px; }
  .bt-qs a { min-height: 40px; }
  .bt-qs .bt-sw { height: 28px; }
}
@media (max-width: 1180px) {
  .bt-band { grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); }
}
@media (max-width: 1100px) {
  .bt-bal__pan li small { display: none; }
}
@media (max-width: 960px) {
  .bt-hero { grid-template-columns: minmax(0, 1fr); grid-template-areas: "txt" "qs" "plate"; }
  .bt-plate__img { width: min(100%, 520px); }
  .bt-qs { padding: 14px 0 0; border-left: 0; border-top: 1px solid var(--rule); }
  .bt-q, .c-burtt .c3q--2 .bt-q, .c-burtt .c3q--4 .bt-q { grid-template-columns: minmax(0, 1fr); grid-template-areas: none; }
  .bt-q__head { grid-area: auto; order: 1; }
  .bt-q__txt { display: contents; }
  .bt-q__txt > .c3q__lede { order: 2; }
  .bt-q__art { grid-area: auto; order: 3; }
  .bt-q__txt > :not(.c3q__lede) { order: 4; }
}
@media (max-width: 640px) {
  .bt-band { grid-template-columns: minmax(0, 1fr); }
  .bt-name { font-size: 84px; }
  .bt-en { font-size: 21px; }
  .bt-who { font-size: 17.5px; }
  .c-burtt .c3q__q { font-size: 28px; }
  .bt-sw--big { min-width: 86px; height: 48px; }
  .bt-sw--big b { font-size: 28px; }
  .bt-bal__stage { height: 330px; }
  .bt-bal__beam { left: 23%; right: 23%; }
  .bt-bal__pan { width: min(170px, 42cqw); }
  .bt-bal__pan li { font-size: 12.5px; padding: 2px 4px; }
  .bt-kp__vs { grid-template-columns: minmax(0, 1fr); }
  .bt-kp__tag { position: static; display: inline-block; margin-bottom: 4px; }
  .bt-kp__stage { aspect-ratio: auto; }
  .bt-kp__cv { height: auto; aspect-ratio: 1; }
  .bt-fig { grid-template-columns: 110px minmax(0, 1fr); }
  .bt-rl__toc ol { grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); }
  .bt-fd__c button { font-size: 13.5px; padding: 5px 8px; gap: 6px; }
  .bt-fd__n { min-width: 1.9em; font-size: 16px; }
  .bt-fd__y { font-size: 14px; }
  .c-burtt .c3q__lede { text-align: left; }
}