.mast-end{justify-self:end;align-items:center;gap:1.1rem;display:flex}.cls-toggle,.cls-tool{color:var(--muted);font:inherit;font-family:var(--mono);letter-spacing:.08em;text-transform:uppercase;white-space:nowrap;cursor:pointer;transition:color .15s, background-color .4s var(--out), box-shadow .4s var(--out), scale .16s var(--out);background:0 0;border:0;border-radius:999px;align-items:center;gap:.5rem;margin:-.42rem 0;padding:.42rem .75rem .4rem .62rem;font-size:11px;line-height:1;text-decoration:none;display:inline-flex;box-shadow:inset 0 0 0 1px #0000}.cls-toggle:hover,.cls-tool:hover{color:var(--ink);box-shadow:inset 0 0 0 1px var(--hair)}.cls-toggle:active,.cls-tool:active{scale:.96}.cls-toggle:focus-visible,.cls-tool:focus-visible,.cls-step:focus-visible{outline:2px solid var(--accent);outline-offset:2px}.cls-ico{fill:none;stroke:currentColor;stroke-width:1.15px;stroke-linecap:round;stroke-linejoin:round;flex:none;width:15px;height:13px}@media (width>=900px){body.is-space .mast-end{--ink:#ece7dc;--muted:#ece7dc8c;--hair:#ece7dc40}}html:not(.is-classroom) .cls-only{display:none!important}.is-classroom{--col:min(46rem, 31vw);--cls-margin:clamp(1.25rem, 5vw, 7rem)}.is-classroom .essay{margin-left:var(--cls-margin)}.is-classroom .mark,.is-classroom .mast-plate,.is-classroom .langs,.is-classroom .rail,.is-classroom .progress,.is-classroom .scroll-cue,.is-classroom .cover-go,.is-classroom .refs,.is-classroom .watch,.is-classroom .related,.is-classroom .next,.is-classroom .back{display:none!important}.is-classroom .mast{grid-template-columns:1fr auto}.is-classroom .mast-end{box-shadow:inset 0 0 0 1px var(--hair-2);-webkit-backdrop-filter:blur(12px);backdrop-filter:blur(12px);--ink:#16140f;--muted:#8b867b;--hair:#16140f24;background:#efebe3b8;border-radius:999px;grid-column:2;gap:.2rem;margin:-.5rem -.35rem;padding:.3rem}.is-classroom .mast-end .cls-toggle,.is-classroom .mast-end .cls-tool{color:var(--ink-2);background:var(--paper-hi);margin:0;padding:.62rem .95rem .6rem .8rem;font-size:12px;box-shadow:inset 0 1px #fffc,0 0 0 1px #16140f0f}.is-classroom .mast-end .cls-toggle:hover,.is-classroom .mast-end .cls-tool:hover{color:var(--paper-hi);background:var(--ink)}.cls-tool i{font-style:normal}.is-classroom .chapter{padding:max(16vh,8.5rem) 0 14vh}.is-classroom .chapter h2{margin:1.2rem 0 1.6rem;font-size:clamp(2.5rem,4.4vw,6.4rem)}.is-classroom .chapter p{max-width:none;color:var(--ink);margin-bottom:1.15rem;font-size:clamp(1.15rem,1.4vw,2rem);line-height:1.5}.is-classroom:lang(zh-Hans) .chapter p{line-height:1.75}.is-classroom .ch-num{font-size:13px}.is-classroom .caption{line-height:1.5;color:var(--ink-2)!important;font-size:13px!important}.is-classroom .cover h1{max-width:8ch;font-size:clamp(3.4rem,7vw,10rem)}.is-classroom:lang(zh-Hans) .cover h1{max-width:5em}.is-classroom .dek{font-size:clamp(1.2rem,1.55vw,2.2rem);line-height:1.5;max-width:none!important}.is-classroom .eyebrow{font-size:12px}.is-classroom .lab-ask{color:var(--ink);font-size:clamp(1.1rem,1.3vw,1.8rem)}.is-classroom .note h3{font-size:clamp(1.9rem,2.6vw,3.6rem)}.is-classroom .notes,.is-classroom .chapter-lab{padding-top:max(16vh,8.5rem)}@media (width>=900px){.is-classroom .stage-caption{max-width:34rem;color:var(--ink);font-size:14px}.is-classroom .hud-k{color:var(--ink-2);font-size:14px}.is-classroom .hud-v{font-size:30px}}@media (width>=1500px){.is-classroom .stage-caption{max-width:38rem;font-size:16px}.is-classroom .hud-k{font-size:16px}.is-classroom .hud-v{font-size:36px}}@media (width>=900px){.is-classroom .topic .stage:after{width:calc(var(--col) + var(--cls-margin) + 9vw);background:linear-gradient(90deg, var(--paper) 0, var(--paper) calc(100% - 9vw), #efebe3d1 calc(100% - 6vw), #efebe34d calc(100% - 2.5vw), #efebe300 100%)}.is-classroom .tag-pill{background:#faf8f3f7;padding:.34rem .85rem .4rem;box-shadow:0 0 0 1px #16140f42,0 12px 26px -14px #16140f80}.is-classroom .tag-pill b,.is-classroom .tags-parts .tag-pill b{font-size:19px}.is-classroom:lang(zh-Hans) .tag-pill b,.is-classroom:lang(zh-Hans) .tags-parts .tag-pill b{font-size:18px}.is-classroom .tag-pill small{color:var(--ink-2);font-size:11.5px}.is-classroom .tag-stem{height:calc(1.4rem + var(--lift,0px))}.is-classroom #scene{--stage-zoom:1.08}}.is-classroom .lab{gap:1.9rem}.is-classroom .lab-key{color:var(--ink);font-size:13px}.is-classroom .lab-value{font-size:16px}.is-classroom .lab-ends{font-size:12px}.is-classroom .lab input[type=range]{height:44px}.is-classroom .lab input[type=range]::-webkit-slider-runnable-track{height:2px}.is-classroom .lab input[type=range]::-webkit-slider-thumb{width:28px;height:28px;margin-top:-13px}.is-classroom .lab input[type=range]::-moz-range-track{height:2px}.is-classroom .lab input[type=range]::-moz-range-thumb{width:28px;height:28px}.is-classroom .lab-option{min-height:48px;padding:.7rem 1.1rem;font-size:16px}.is-classroom .lab-toggle{min-height:56px;padding:.95rem 0;font-size:16px}.is-classroom .lab-toggle .lab-key{font-size:13px}.is-classroom .lab-switch{width:42px;height:24px}.is-classroom .lab-switch:after{width:16px;height:16px;top:4px;left:4px}.is-classroom .lab-toggle[aria-pressed=true] .lab-switch:after{transform:translate(18px)}.is-classroom .lab-link{align-items:center;min-height:48px;font-size:18px}.is-classroom .lab-play{padding:1.35rem 1.5rem;font-size:1.85rem}.is-classroom:lang(zh-Hans) .lab-play{font-size:1.55rem}.is-classroom .lab-readouts{gap:.55rem 1rem;font-size:14px}.is-classroom .lever{height:3.8rem}.is-classroom .lever-slot{height:8px;margin-top:-4px}.is-classroom .lever-handle{border-radius:.8rem;width:1.6rem;height:3.2rem;margin-top:-1.6rem;left:-.8rem}.is-classroom .lever-handle b{top:.8rem;bottom:.8rem}.is-classroom .lever-detents{height:2.6rem}.is-classroom .lever-detents button{padding:.6rem .5rem;font-size:13px}.is-classroom .lab select,.is-classroom .lab input[type=text],.is-classroom .lab button:not([class^=lab-]):not(.lever-detents button){min-height:48px;font-size:16px}.is-classroom .split-handle{width:4.6rem;height:4.6rem;margin:-2.3rem 0 0 -2.3rem}.cls-dock{z-index:31;left:var(--cls-margin);max-width:calc(var(--col) + 2rem);pointer-events:none;grid-template-columns:minmax(0,auto);justify-items:start;gap:.6rem;display:grid;position:fixed;top:.8rem}.cls-dock:before{content:"";z-index:-1;top:-.8rem;left:calc(-1 * var(--cls-margin));width:calc(var(--col) + var(--cls-margin));pointer-events:none;background:linear-gradient(var(--paper) calc(100% - 2.6rem), #efebe300);height:calc(100% + 3.4rem);position:absolute}.cls-dock>*{pointer-events:auto}.cls-dock-core{background:#16140f0b;border-radius:999px;align-items:center;gap:.25rem;max-width:100%;padding:.32rem;display:flex;box-shadow:inset 0 0 0 1px #16140f14}.cls-step{background:var(--paper-hi);width:3.4rem;height:3.4rem;color:var(--ink);cursor:pointer;transition:background-color .15s, color .15s, scale .16s var(--out), opacity .3s var(--out);border:0;border-radius:50%;flex:none;place-items:center;padding:0;display:grid;box-shadow:inset 0 1px #ffffffd9,0 1px 2px #16140f0f,0 12px 24px -16px #16140f73}.cls-step:hover{background:var(--ink);color:var(--paper-hi)}.cls-step:active{scale:.93}.cls-step:disabled{opacity:.32;cursor:default;pointer-events:none}.cls-step svg{fill:none;stroke:currentColor;stroke-width:1.4px;stroke-linecap:round;stroke-linejoin:round;width:18px;height:18px}.cls-where{align-items:baseline;gap:.9rem;min-width:0;margin:0;padding:0 1rem;display:flex}.cls-count{color:var(--muted);flex:none;align-items:baseline;gap:.35rem;font-size:12px;display:inline-flex}.cls-count b{color:var(--accent);font-size:16px;font-weight:400;display:inline-block}.cls-title{min-width:0;font-family:var(--serif);white-space:nowrap;text-overflow:ellipsis;color:var(--ink);font-size:1.25rem;line-height:1.2;display:block;overflow:hidden}:lang(zh-Hans) .cls-title{font-size:1.1rem;font-weight:500}.cls-foot{align-items:center;gap:1.1rem;padding:0 1.3rem;display:flex}.cls-ticks{flex-wrap:wrap;gap:5px;display:flex}.cls-ticks i{background:var(--hair);width:1.15rem;height:2px;transition:background-color .5s var(--out);border-radius:1px}.cls-ticks i.on{background:var(--ink)}.cls-ticks i.now{background:var(--accent)}.cls-keys{color:var(--muted);white-space:nowrap;margin:0;font-size:10.5px}@media (hover:none){.cls-keys{display:none}}@media (width>=1500px){.cls-step{width:3.8rem;height:3.8rem}.cls-count{font-size:14px}.cls-count b{font-size:22px}.cls-title{font-size:1.6rem}:lang(zh-Hans) .cls-title{font-size:1.4rem}.cls-ticks i{border-radius:1.5px;width:1.35rem;height:3px}.cls-keys{font-size:12px}.is-classroom .mast-end .cls-toggle,.is-classroom .mast-end .cls-tool{padding:.7rem 1.05rem .68rem .9rem;font-size:13px}.is-classroom .cls-ico{width:17px;height:15px}}.teach-link{box-shadow:inset 0 0 0 1px var(--hair-2);transition:background-color .4s var(--out);background:#16140f0a;border-radius:1.4rem;grid-template-columns:1fr auto;align-items:center;gap:.4rem 1.2rem;padding:1.3rem 1.4rem 1.35rem;text-decoration:none;display:grid}.teach-link:hover{background:#16140f12}.teach-link-k{color:var(--accent)}.teach-link-t{color:var(--ink-2);grid-column:1;font-size:15px;line-height:1.55}.teach-link-go{background:var(--ink);width:2.6rem;height:2.6rem;color:var(--paper-hi);transition:translate .5s var(--out);border-radius:50%;grid-area:1/2/span 2;place-items:center;display:grid}.teach-link:hover .teach-link-go{translate:.2rem}.is-classroom .teach-link-t{color:var(--ink);font-size:clamp(1rem,1.15vw,1.5rem)}html.vt-classroom::view-transition-old(root){animation:.16s cubic-bezier(.3,0,.8,.15) both cls-fade-out}html.vt-classroom::view-transition-new(root){animation:.36s cubic-bezier(.23,1,.32,1) both cls-fade-in}@keyframes cls-fade-out{to{opacity:0}}@keyframes cls-fade-in{0%{opacity:0}}@media (width<=899px){.mast-end{gap:.9rem}.is-classroom .chapter{padding:2.4rem 0 2rem}.is-classroom .chapter h2{font-size:clamp(2.1rem,9.6vw,2.9rem)}.is-classroom .chapter p{font-size:1.12rem}.is-classroom .cover h1,.is-classroom:lang(zh-Hans) .cover h1{max-width:none;font-size:clamp(2.9rem,13vw,4.2rem)}.is-classroom .dek{font-size:1.12rem}.is-classroom .essay{margin-left:0;padding-bottom:6.5rem}.is-classroom .mast-end{margin:-.3rem -.4rem}.is-classroom .mast-end .cls-toggle,.is-classroom .mast-end .cls-tool{padding:.62rem .8rem}.cls-dock{top:auto;left:var(--gutter);right:var(--gutter);bottom:max(.75rem, env(safe-area-inset-bottom));grid-template-columns:minmax(0,1fr);max-width:none}.cls-dock:before{content:"";z-index:-1;left:calc(-1 * var(--gutter));right:calc(-1 * var(--gutter));pointer-events:none;background:linear-gradient(to top, var(--paper) calc(100% - 2.75rem), #efebe3db calc(100% - 1.6rem), #efebe300);position:absolute;top:-2.75rem;bottom:-3rem}.cls-dock-core{background:#efebe3f0;width:100%;box-shadow:inset 0 0 0 1px #16140f1a,0 14px 30px -18px #16140f73}.cls-where{flex-direction:column;flex:1;align-items:flex-start;gap:.1rem;padding:0 .5rem}.cls-title{max-width:100%}.cls-foot{display:none}}@media (width<=599px){.is-classroom .mast-end .cls-tool [data-label],.is-classroom .mast-end .cls-tool .cls-word{clip-path:inset(50%);white-space:nowrap;width:1px;height:1px;position:absolute;overflow:hidden}}