@charset "UTF-8";
:root{--bg:#f6f7f2;--paper:#fff;--ink:#243b37;--muted:#74817b;--green:#215c50;--light:#e9f0e7;--lime:#d5e7a8;--line:#e3e7df;--coral:#c97456;--soft:#fbf0e8;--radius:22px;font-family:Inter,"Segoe UI","Microsoft YaHei",system-ui,sans-serif;color:var(--ink);background:var(--bg);font-synthesis:none}*{box-sizing:border-box}body{margin:0;line-height:1.75}button,input,textarea{font:inherit}button,a{-webkit-tap-highlight-color:transparent}button{cursor:pointer;color:inherit;border:0}button:disabled{cursor:default;opacity:.52}button:focus-visible,a:focus-visible,textarea:focus-visible,summary:focus-visible{outline:3px solid var(--coral);outline-offset:4px}a{color:var(--green)}svg{max-width:100%;height:auto}h1,h2,h3,p{margin:0}h1{font-size:clamp(28px,3.2vw,40px);line-height:1.4;letter-spacing:-1px;font-weight:650}h2{font-size:23px;line-height:1.5;font-weight:650}h3{font-size:18px;line-height:1.5}small{font-size:12px}.skip{position:fixed;top:-100px;left:20px;background:var(--paper);padding:10px;z-index:100}.skip:focus{top:10px}.shell{min-height:100vh}.sidebar{position:fixed;width:244px;left:0;top:0;bottom:0;border-right:1px solid var(--line);padding:34px 25px;display:flex;flex-direction:column;background:#f3f5ee}.brand{display:flex;gap:11px;align-items:center;text-decoration:none;color:var(--ink)}.brand img{width:39px;height:39px}.brand strong{display:block;font-size:19px;letter-spacing:2px}.brand small{display:block;letter-spacing:2px;color:var(--muted);font-size:10px}.side-label{font-size:11px;color:var(--muted);letter-spacing:2px;margin:44px 12px 15px}.nav{display:flex;flex-direction:column;gap:8px}.nav button{text-align:left;padding:12px 16px;border-radius:12px;background:transparent;display:flex;gap:12px;align-items:center}.nav button.active{background:var(--green);color:#fff}.nav button:hover:not(.active){background:var(--light)}.nav-icon{width:23px;font-size:19px}.side-bottom{margin-top:auto;font-size:12px;color:var(--muted);border-top:1px solid var(--line);padding:20px 8px 0}.side-bottom strong{font-weight:500;color:var(--ink);display:block;margin-bottom:6px}.workspace{margin-left:244px;padding:0 46px 80px}.topbar{height:91px;display:flex;justify-content:space-between;align-items:center;border-bottom:1px solid var(--line);gap:16px;font-size:13px;color:var(--muted)}.topbar .tag{display:flex;align-items:center;gap:8px}.dot{width:6px;height:6px;border-radius:50%;background:#77a48a;display:inline-block}.mobile-brand{display:none}main{max-width:1050px;margin:38px auto 0}.eyebrow{font-size:11px;letter-spacing:2.4px;text-transform:uppercase;color:var(--green);font-weight:650;margin-bottom:12px}.lead{color:#677970;font-size:15px;line-height:1.95;margin-top:15px;max-width:560px}.hero{display:grid;grid-template-columns:1.15fr 1fr;align-items:center;gap:20px;background:#ecf1e5;border:1px solid #e1e8d6;border-radius:28px;overflow:hidden;padding:40px 40px 30px}.hero .art{min-width:0}.hero .art svg{width:100%;display:block}.hero .actions{margin-top:26px}.actions{display:flex;align-items:center;gap:10px;flex-wrap:wrap}.btn{display:inline-flex;justify-content:center;align-items:center;gap:9px;min-height:46px;border-radius:12px;padding:10px 19px;font-weight:550;font-size:14px;line-height:1.6;background:var(--green);color:#fff;text-decoration:none}.btn:hover{background:#174a40}.btn.secondary{background:#fff;color:var(--green);border:1px solid #d6dfd3}.btn.ghost{background:transparent;color:var(--green);border:1px solid #d4ddd1}.btn.slim{min-height:38px;padding:7px 14px;font-size:13px}.pill{display:inline-flex;align-items:center;gap:6px;border-radius:30px;padding:3px 10px;background:#f3f6ed;color:var(--green);font-size:11px;border:1px solid #e0e6d6}.hero-meta{font-size:12px;color:var(--muted);margin-top:18px}.section-head{display:flex;justify-content:space-between;align-items:center;gap:12px;margin:30px 0 16px}.section-head h2{font-size:19px}.section-head span{font-size:12px;color:var(--muted)}.two-col{display:grid;grid-template-columns:1fr 1fr;gap:18px}.card{background:var(--paper);border:1px solid var(--line);border-radius:var(--radius);padding:25px}.card .sub{color:var(--muted);font-size:13px;margin-top:8px}.card-num{font-family:Georgia,serif;font-size:38px;color:var(--green);line-height:1}.card-top{display:flex;justify-content:space-between;align-items:start;gap:12px;margin-bottom:15px}.line-progress{height:5px;background:#edf0e8;border-radius:5px;overflow:hidden;margin:17px 0 10px}.line-progress span{height:100%;display:block;background:#91b183;border-radius:5px}.text-link{padding:8px 0;background:none;color:var(--green);font-size:13px;min-height:40px}.steps-preview{display:flex;gap:20px;margin-top:14px;font-size:12px;color:var(--muted)}.steps-preview span:before{content:'·';margin-right:7px;color:var(--coral)}.unit{border:1px solid var(--line);background:var(--paper);border-radius:16px;margin:12px 0;overflow:hidden}.unit summary{list-style:none;cursor:pointer;display:flex;align-items:center;gap:17px;padding:20px}.unit summary::-webkit-details-marker{display:none}.unit-number{background:#eef2e8;color:var(--green);width:40px;height:40px;border-radius:12px;display:grid;place-items:center;font-family:Georgia,serif;flex-shrink:0}.unit summary small{display:block;color:var(--muted)}.unit summary .arrow{margin-left:auto;color:var(--muted)}.unit-lessons{padding:0 20px 17px 77px}.lesson-link{width:100%;display:flex;justify-content:space-between;gap:15px;text-align:left;background:#eff4e9;border-radius:12px;padding:14px 16px;font-size:14px}.planned{font-size:13px;color:var(--muted);padding:12px 0;border-bottom:1px dashed var(--line)}.banner{border-radius:16px;background:var(--soft);padding:16px 20px;font-size:13px;color:#82614f;margin:20px 0}.home-footer{margin-top:35px;padding-top:20px;border-top:1px solid var(--line);font-size:12px;color:var(--muted);display:flex;justify-content:space-between;gap:14px}.mobile-nav{display:none}.course-head{margin-bottom:25px}.course-head h1{font-size:27px}.course-head p{font-size:13px;color:var(--muted);margin-top:8px}.lesson-layout{display:grid;grid-template-columns:minmax(0,1fr) 206px;gap:22px;align-items:start}.lesson-panel{background:white;border-radius:24px;border:1px solid var(--line);padding:32px;min-width:0}.lesson-label{font-size:12px;color:var(--muted);display:flex;justify-content:space-between;align-items:center;gap:10px;margin-bottom:20px}.lesson-panel h2{font-size:26px;letter-spacing:-.4px}.body-copy{font-size:16px;line-height:1.95;margin:16px 0 20px;color:#4a6057}.body-copy p+p{margin-top:12px}.visual{border-radius:18px;background:#f2f5ed;overflow:hidden;padding:12px;margin:21px 0}.visual svg{display:block;width:100%;max-height:270px}.caption{font-size:11px;color:var(--muted);text-align:center;margin:6px 4px}.scene-control{display:flex;gap:7px;flex-wrap:wrap;justify-content:center;margin:10px 0}.scene-control button{padding:7px 14px;border:1px solid #d6e0d2;background:white;border-radius:30px;font-size:12px;min-height:38px}.scene-control button.selected{background:var(--green);color:white;border-color:var(--green)}.insight{font-size:14px;line-height:1.85;border-left:3px solid #adc780;background:#f4f7ee;padding:13px 16px;margin:17px 0}.quiz{border-top:1px solid var(--line);padding-top:22px;margin-top:24px}.quiz-title{font-size:16px;font-weight:600;margin-bottom:13px}.quiz-kicker{font-size:11px;letter-spacing:1px;color:var(--green);margin-bottom:7px}.options{display:flex;flex-direction:column;gap:9px}.option{display:flex;gap:12px;text-align:left;width:100%;padding:13px 15px;background:#fff;border:1px solid #dfe5dc;border-radius:12px;line-height:1.7;font-size:14px;align-items:center;min-height:50px}.option .letter{border:1px solid #dce3d6;color:var(--muted);border-radius:7px;flex:0 0 25px;height:25px;display:grid;place-items:center;font-size:11px}.option:hover{background:#f6f8f1}.option.chosen{border-color:var(--green);background:#f0f5e9}.option.correct{border-color:#87ab7a;background:#eef6e8}.option.wrong{border-color:#dba384;background:#fff4eb}.option.chosen .letter{background:var(--green);color:white;border-color:var(--green)}.quiz-actions{display:flex;gap:12px;align-items:center;flex-wrap:wrap;margin-top:14px}.feedback{margin-top:13px;border-radius:12px;padding:13px 16px;font-size:14px;line-height:1.85;background:#edf5e8;color:#345d37}.feedback.retry{background:#fcf1e6;color:#835e3b}.feedback.neutral{background:#edf1f6;color:#4a627a}.feedback strong{display:block;margin-bottom:3px}.hint{padding:12px 15px;background:#fff9e9;border-radius:12px;font-size:13px;margin-top:12px;color:#806946}.next-row{display:flex;justify-content:space-between;align-items:center;gap:12px;border-top:1px solid var(--line);margin-top:30px;padding-top:22px}.progress-note{font-size:12px;color:var(--muted);margin-bottom:10px}.rail{position:sticky;top:20px;background:#edf1e8;border:1px solid #e0e7d8;border-radius:18px;padding:19px 14px}.rail h3{font-size:13px;margin:0 10px 13px}.rail button{width:100%;padding:8px 10px;background:transparent;display:flex;text-align:left;align-items:center;gap:9px;color:var(--muted);border-radius:8px;font-size:12px;min-height:36px}.rail button.current{background:white;color:var(--green);font-weight:600}.rail .index{font-size:10px;width:18px;height:18px;flex-shrink:0;border-radius:50%;background:#e0e7d8;display:grid;place-items:center}.rail button.current .index{background:var(--green);color:white}.rail-foot{font-size:11px;color:var(--muted);padding:15px 10px 0;border-top:1px solid #dfe5d8;margin-top:12px}.memory-card{border:1px solid #dce4ce;background:#f5f8ee;border-radius:17px;padding:20px;margin:12px 0}.memory-card .number{color:#91a776;font-family:Georgia,serif;font-size:24px;margin-bottom:6px}.memory-card h3{font-size:17px}.memory-card p{font-size:14px;margin-top:9px;color:#62745c}.recall{padding:20px;border:1px solid var(--line);border-radius:16px;margin:14px 0}.recall p{font-size:15px;margin-bottom:13px}.recall .answer{background:#eef4e6;padding:12px 15px;border-radius:10px;font-size:14px;margin:14px 0}.rating{display:flex;gap:7px;flex-wrap:wrap}.rating button{font-size:12px;padding:8px 12px;border:1px solid #dce3d5;border-radius:9px;background:white;min-height:40px}.rating button.selected{border-color:var(--green);background:var(--light)}.note-label{display:block;font-size:13px;font-weight:600;margin:18px 0 9px}textarea{width:100%;min-height:110px;resize:vertical;border:1px solid #dce3d8;border-radius:12px;padding:13px;background:white;color:var(--ink);font-size:14px;line-height:1.8}.tiny{font-size:12px;color:var(--muted);margin-top:8px}.summary-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:10px;margin:20px 0}.summary-item{padding:15px 10px;text-align:center;background:#f0f4e9;border-radius:12px;font-size:12px}.summary-item strong{display:block;color:var(--green);font-size:25px}.empty{padding:30px;text-align:center;background:white;border:1px solid var(--line);border-radius:20px}.empty p{color:var(--muted);margin:10px auto 20px;max-width:450px;font-size:14px}.subsection{margin-top:28px}.source{font-size:12px;color:var(--muted);line-height:1.9}.source summary{cursor:pointer;padding:12px 0}.source p{margin:8px 0}.toast{position:fixed;bottom:30px;left:50%;transform:translateX(-50%);background:#27483e;color:#fff;padding:10px 18px;border-radius:12px;z-index:20;font-size:13px;max-width:90vw}.storage-alert{background:#fff0df;color:#83582b;font-size:13px;padding:12px;text-align:center}.main-focus:focus{outline:none}.split-stat{display:flex;gap:15px;align-items:center}.review-count{font:42px Georgia,serif;color:var(--green)}.glow{animation:glow 2s infinite alternate}.bubble{animation:bubble 2.5s infinite;transform-box:fill-box;transform-origin:center}.bubble:nth-child(2n){animation-delay:-1s}.paused .bubble,.paused .glow{animation-play-state:paused}@keyframes bubble{from{transform:translateY(8px);opacity:.25}to{transform:translateY(-18px);opacity:1}}@keyframes glow{to{opacity:.6}}@media(prefers-reduced-motion:reduce){*,*:before,*:after{animation:none!important;scroll-behavior:auto!important}}
@media(min-width:1500px){.workspace{padding-left:70px;padding-right:70px}}
@media(max-width:1100px){.workspace{padding:0 25px 65px;margin-left:210px}.sidebar{width:210px;padding:30px 18px}.hero{padding:30px}.lesson-layout{grid-template-columns:minmax(0,1fr)}.rail{position:static;display:none}.lesson-panel{padding:28px}}
@media(max-width:760px){.sidebar{display:none}.workspace{margin:0;padding:0 18px 100px}.topbar{height:73px}.topbar .breadcrumb{display:none}.mobile-brand{display:flex}.mobile-brand .brand img{width:31px;height:31px}.mobile-brand .brand strong{font-size:16px;letter-spacing:1px}.mobile-brand .brand small{display:none}.topbar .tag{font-size:11px}main{margin-top:25px}.hero{grid-template-columns:1fr;padding:27px 24px 8px;border-radius:23px;gap:0}.hero h1{font-size:32px}.hero .lead{font-size:14px;margin-top:12px}.hero .actions{margin-top:20px}.hero .art{margin:0 auto;width:100%;max-width:330px}.hero .art svg{max-height:195px}.hero-meta{font-size:11px}.two-col{gap:12px}.card{padding:19px;border-radius:18px}.two-col .card h3{font-size:15px}.two-col .card .sub{font-size:12px}.card .btn{padding:9px 12px;font-size:12px;min-height:42px}.steps-preview{gap:11px;font-size:11px;flex-wrap:wrap}.section-head{margin-top:24px}.section-head h2{font-size:18px}.section-head span{font-size:11px}.home-footer{display:block}.home-footer span{display:block;margin-top:6px}.mobile-nav{position:fixed;bottom:0;left:0;right:0;background:#fcfdf9f5;backdrop-filter:blur(12px);display:grid;grid-template-columns:repeat(4,1fr);padding:7px 9px calc(7px + env(safe-area-inset-bottom));border-top:1px solid var(--line);z-index:10}.mobile-nav button{background:transparent;color:#8a958b;font-size:10px;padding:4px;min-height:46px}.mobile-nav button span{display:block;font-size:19px;line-height:1.4}.mobile-nav button.active{color:var(--green);font-weight:650}.course-head h1{font-size:23px}.lesson-panel{padding:22px 18px;border-radius:20px}.lesson-panel h2{font-size:23px}.body-copy{font-size:15px}.quiz-title{font-size:15px}.option{font-size:14px;padding:12px}.next-row .btn{font-size:13px;padding:11px 14px}.lesson-label{font-size:11px}.visual{padding:5px;margin:17px 0}.caption{font-size:10px}.summary-grid{gap:6px}.summary-item{font-size:11px}.summary-item strong{font-size:22px}.unit summary{padding:16px;gap:12px}.unit-lessons{padding:0 16px 16px}.unit summary h3{font-size:16px}.unit-number{width:35px;height:35px}.toast{bottom:90px}.banner{font-size:12px}.eyebrow{font-size:10px}.recall{padding:16px}.memory-card{padding:17px}}

/* Refined illustration system, v0.2 */
.course-illustration{margin:0;position:relative}
.course-illustration img{display:block;width:100%;height:auto;border-radius:22px;box-shadow:0 13px 34px #536f5220}
.course-illustration figcaption{font-size:11px;color:#61765c;text-align:center;margin-top:12px;letter-spacing:1px}
.experiment-gallery{margin:24px 0;border:1px solid #dce4d8;background:#f6f7f1;border-radius:20px;padding:16px;overflow:hidden}
.observation-kicker{display:flex;justify-content:space-between;gap:12px;color:var(--green);font-size:12px;font-weight:600;padding:0 2px 13px}
.observation-kicker span{font-size:10px;color:var(--muted);font-weight:400}
.experiment-grid{display:grid;grid-template-columns:minmax(0,1fr);gap:12px}
.experiment-grid.compare{grid-template-columns:repeat(2,minmax(0,1fr))}
.comparison-help{font-size:12px;color:#65776b;margin:0 2px 12px}
.experiment-grid.focus-one{grid-template-columns:minmax(0,1fr)}
.experiment-grid.focus-one .experiment-card:not(.enlarged){display:none}
.experiment-card.enlarged svg{max-height:460px}
.experiment-grid:not(.compare) .figure-inspect{display:none}
.figure-inspect{display:block;width:calc(100% - 24px);min-height:44px;margin:0 12px 12px;border:1px solid #ceddce;border-radius:10px;background:#f0f5ec;color:var(--green);font-size:12px}
.experiment-meta{display:flex;justify-content:space-between;align-items:center;gap:4px;font-size:10px;color:#7d907f;line-height:1.5}
.experiment-heading .scene-type{display:inline-block;font-size:10px;letter-spacing:0;padding:2px 6px;border-radius:5px;background:#eef3e9;color:#647c67;white-space:nowrap}
.experiment-card[data-dynamic="false"] .scene-type{background:#f0f0eb;color:#727a70}
.experiment-card{min-width:0;margin:0;border:1px solid #dbe4d7;border-radius:15px;background:#fdfdf8;overflow:hidden}
.experiment-heading{padding:13px 16px 9px;background:#ffffff80}
.experiment-heading>span{font-size:10px;color:#7d907f;letter-spacing:1.5px}
.experiment-heading h3{font-size:16px;font-weight:600;margin:3px 0;color:#365b4e}
.experiment-card svg{display:block;width:100%;height:auto;max-height:335px}
.experiment-card figcaption{font-size:12px;line-height:1.8;color:#63766a;padding:12px 15px;min-height:66px}
.figure-key{display:inline-grid;place-items:center;width:19px;height:19px;margin-right:3px;border:1px solid #aec2b2;border-radius:50%;font-size:11px;color:var(--green);vertical-align:baseline}
.illustration-toolbar{display:flex;justify-content:space-between;align-items:center;gap:10px;margin-top:13px;flex-wrap:wrap}
.illustration-toolbar button{min-height:44px;padding:8px 15px;background:#fff;border:1px solid #ccdccc;border-radius:12px;color:var(--green);font-size:12px}
.illustration-toolbar button span{display:inline-block;width:15px}
.illustration-toolbar small{font-size:10px;color:#7d8c7e}
.illustration-toolbar .motion-preference-note{display:none}
.motion-status,.motion-detail,.static-scene-note,.motion-preference-note{font-size:12px;line-height:1.8;color:#64786a}
.motion-detail{margin-top:12px}
.static-scene-note{padding:6px 0}
.observation-controls{margin-bottom:12px}
.observation-controls .scene-control{justify-content:flex-start;margin:0 0 8px}
.observation-controls .illustration-toolbar{justify-content:flex-start;margin:0;gap:12px}
.focus-static-note{display:none;font-size:12px;line-height:1.8;color:#64786a;padding:6px 0}
.experiment-gallery[data-focus-static="true"] .illustration-toolbar{display:none}
.experiment-gallery[data-focus-static="true"] .focus-static-note{display:block}
.scene-control button{min-height:44px}
.observation-prompt{font-size:13px;line-height:1.85;background:#eaf0e3;border-radius:11px;padding:13px 15px;margin-top:14px;color:#4b6450}
.experiment-gallery .caption{margin-top:12px;font-size:10px}
.experiment-gallery .stage-switch{margin-bottom:0}
.rise{animation:rise var(--duration,3s) var(--delay,0s) infinite linear}
.water-ring{transform-box:fill-box;transform-origin:center;animation:water-ring 3.6s ease-out infinite}
.soft-glow{animation:soft-glow 4.5s ease-in-out infinite alternate}
.white-burn{transform-box:fill-box;transform-origin:center;animation:white-burn 3.4s ease-in-out infinite alternate}
.candle-flame{transform-box:fill-box;transform-origin:50% 100%;animation:candle-flame 3.6s ease-in-out infinite}
.wax-pool{animation:wax-pool 5s ease-in-out infinite alternate}
.smoke{animation:smoke 4.2s ease-in-out infinite}
.condensation{transform-box:fill-box;transform-origin:50% 0;animation:condensation 4s var(--delay,0s) ease-in-out infinite}
.heat-shimmer{animation:heat-shimmer 4s ease-in-out infinite}
.filament{animation:soft-glow 5s ease-in-out infinite alternate}
.experiment-gallery.paused *{animation-play-state:paused!important}
@keyframes rise{0%{transform:translateY(12px);opacity:.4}80%{opacity:.9}100%{transform:translateY(calc(-1 * var(--travel)));opacity:0}}
@keyframes water-ring{0%{transform:scale(.6);opacity:.1}35%{opacity:.45}100%{transform:scale(2.5);opacity:0}}
@keyframes soft-glow{from{opacity:.65}to{opacity:.95}}
@keyframes white-burn{from{transform:scale(.97);opacity:.9}to{transform:scale(1.04);opacity:1}}
@keyframes candle-flame{0%,100%{transform:rotate(-1deg) scaleX(1)}45%{transform:rotate(1.8deg) scaleX(.95)}75%{transform:rotate(-.4deg) scaleY(.97)}}
@keyframes wax-pool{from{opacity:.75}to{opacity:1}}
@keyframes smoke{0%,100%{transform:translateY(0);opacity:.45}50%{transform:translateY(-9px);opacity:.7}}
@keyframes condensation{0%{transform:translateY(-2px) scale(.45);opacity:.35}65%{transform:translateY(2px) scale(1);opacity:.95}90%{transform:translateY(17px) scale(.85);opacity:.6}100%{transform:translateY(24px) scale(.8);opacity:0}}
@keyframes heat-shimmer{0%,100%{opacity:.3}50%{opacity:.65}}
@media(max-width:760px){
 .hero .art{max-width:100%;margin:24px 0 14px}
 .course-illustration img{border-radius:17px}
 .experiment-gallery{padding:10px;margin:19px 0;border-radius:17px}
 .experiment-grid.compare{grid-template-columns:repeat(2,minmax(0,1fr));gap:8px;align-items:start}
 .experiment-grid.compare.focus-one{grid-template-columns:minmax(0,1fr)}
 .experiment-grid.compare .experiment-heading{padding:10px 9px 7px}
 .experiment-grid.compare .experiment-heading h3{font-size:14px;min-height:42px;display:flex;align-items:center}
 .experiment-grid.compare .experiment-heading>span{font-size:10px;letter-spacing:.5px}
 .experiment-grid.compare .experiment-card figcaption{padding:10px 9px;font-size:12px;line-height:1.75}
 .experiment-grid.compare.focus-one .experiment-heading h3{min-height:0;font-size:16px}
 .experiment-grid.compare .figure-inspect{width:calc(100% - 16px);margin:0 8px 10px;font-size:11px}
 .experiment-card svg{max-height:none}
 .experiment-grid.focus-one .experiment-card svg{max-height:250px}
 .experiment-grid:not(.compare) .experiment-card svg{max-height:250px}
 .experiment-heading{padding:12px 15px 9px}
 .experiment-heading h3{font-size:16px}
 .experiment-card figcaption{font-size:12px;min-height:0}
 .illustration-toolbar small{display:none}
 .observation-prompt{font-size:13px;padding:11px 12px}
}
@media(prefers-reduced-motion:reduce){
 .experiment-gallery *{animation:none!important}
 .illustration-toolbar button,.illustration-toolbar small,.illustration-toolbar .motion-status{display:none}
 .illustration-toolbar .motion-preference-note{display:block;font-size:12px}
}