:root{--bg:#f8fafc;--ink:#111827;--sub:#64748b;--line:#e2e8f0;--accent:#635bff;--soft:#eeedff;--white:#fff;--dark:#151b2d}*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--bg);color:var(--ink);font-family:Inter,ui-sans-serif,system-ui,-apple-system,"Segoe UI",sans-serif;font-size:14px}button,input,select{font:inherit}button{cursor:pointer}a{text-decoration:none;color:inherit}.topbar{position:sticky;top:0;z-index:10;background:#fffffff0;backdrop-filter:blur(16px);border-bottom:1px solid var(--line);display:flex;align-items:center;justify-content:space-between;padding:14px max(24px,calc((100vw - 1250px)/2));gap:18px}.brand{font-size:20px;font-weight:850;letter-spacing:-1px;white-space:nowrap}.brandicon{display:inline-grid;place-items:center;background:var(--accent);color:white;border-radius:9px;width:31px;height:31px;margin-right:5px}.accent{color:var(--accent)}.nav{display:flex;gap:7px}.nav a{padding:10px 15px;border-radius:9px;color:#64748b;font-weight:650;white-space:nowrap}.nav a.active,.nav a:hover{background:var(--soft);color:var(--accent)}.iconbtn{border:1px solid var(--line);background:#fff;border-radius:9px;padding:9px 11px;white-space:nowrap}.page{max-width:1250px;margin:0 auto;padding:48px 24px 72px;min-height:75vh}.page[hidden],section[hidden],div[hidden],a[hidden]{display:none!important}.hero{display:grid;grid-template-columns:1fr 1fr;gap:42px;align-items:center;padding:48px 0 65px}.eyebrow{font-size:11px;letter-spacing:2px;font-weight:850;color:var(--accent)}h1{font-size:clamp(34px,5vw,62px);line-height:1.09;letter-spacing:-2.5px;margin:16px 0 20px}h2{font-size:29px;letter-spacing:-1px;margin:9px 0 12px}h3{font-size:16px;letter-spacing:-.3px}p{line-height:1.75;color:#526076}.hero p{font-size:17px;max-width:520px}.actions,.toolbar,.playbar,.democontrols{display:flex;align-items:center;gap:9px;flex-wrap:wrap}.actions{margin-top:24px}.between{justify-content:space-between}.btn{display:inline-flex;align-items:center;justify-content:center;gap:7px;border:1px solid var(--line);border-radius:10px;padding:12px 18px;background:#fff;font-weight:750;color:var(--ink);transition:transform .15s,background .15s}.btn:hover{transform:translateY(-1px);background:#f1f2ff}.btn.primary{background:var(--accent);border-color:var(--accent);color:white}.btn.primary:hover{background:#5047df}.btn.small{padding:8px 12px;font-size:12px}.btn.full{width:100%;margin:12px 0}.stats{display:flex;gap:26px;margin-top:42px;color:var(--sub);font-size:12px}.stats strong{font-size:19px;color:var(--ink);display:block}.heroart{position:relative;background:var(--dark);border-radius:24px;overflow:hidden;box-shadow:0 30px 70px #11182725}.heroart canvas{width:100%;display:block}.artlabel{position:absolute;left:24px;bottom:20px;color:#aeb8d0;letter-spacing:2px;font-size:10px;font-weight:800}.live{color:#26c998}.artlabel .live{margin-left:10px}.sectiontitle{margin:12px 0 20px}.steps{display:grid;grid-template-columns:repeat(3,1fr);gap:15px}.steps article,.notice,.detailpanel,.sidepanel,.quizbox{background:#fff;border:1px solid var(--line);border-radius:15px}.steps article{padding:25px}.steps b{font-size:11px;color:var(--accent);letter-spacing:1px}.steps p{margin-bottom:0}.notice{padding:19px 22px;margin-top:25px;color:#536179;line-height:1.7}.pagehead{margin:5px 0 29px}.pagehead h1{font-size:clamp(33px,4vw,48px);margin:10px 0}.pagehead p{max-width:700px}.progress{max-width:300px}.progress>span{font-size:12px;color:var(--sub)}.track{height:6px;background:var(--line);border-radius:20px;margin-top:8px;overflow:hidden}.track>div{height:100%;width:0;background:var(--accent);transition:width .2s}.learnlayout{display:grid;grid-template-columns:255px minmax(0,1fr);gap:18px;align-items:start}.principlelist{display:grid;gap:5px}.principlelist button{width:100%;border:1px solid transparent;background:transparent;border-radius:10px;text-align:left;padding:12px 11px;display:flex;align-items:center;gap:12px;font-weight:650}.principlelist button:hover,.principlelist button.active{background:var(--soft);color:var(--accent)}.principlelist .index{width:28px;height:28px;flex-shrink:0;display:grid;place-items:center;background:#e9edf3;color:#5e6a7b;border-radius:8px;font-size:11px}.principlelist .active .index{background:var(--accent);color:#fff}.principlelist .done{margin-left:auto;color:#12a77e}.detailpanel{padding:26px}.detailhead{display:flex;justify-content:space-between;gap:15px;align-items:start}.detailhead h2{margin-bottom:4px}.muted{color:var(--sub)}.chip{background:#f1f5f9;color:#64748b;border-radius:50px;padding:7px 10px;font-size:11px;white-space:nowrap}.demobox{background:var(--dark);border-radius:15px;overflow:hidden;margin:23px 0}.demobox canvas{display:block;width:100%;height:auto;aspect-ratio:780/360}.democontrols{background:#20283b;padding:12px 15px;color:white}.sliderlabel{display:flex;align-items:center;gap:9px;flex:1;justify-content:end;font-size:12px}.sliderlabel input{max-width:170px}.sliderlabel output{min-width:40px}.explain p{margin:7px 0 19px}.tip{padding:14px 17px;background:#f0efff;border-left:3px solid var(--accent);border-radius:6px;color:#4c4b78;line-height:1.6}.labtabs{display:flex;gap:10px;margin-bottom:18px}.tab{border:1px solid var(--line);background:white;border-radius:11px;padding:13px 20px;font-weight:800}.tab.active{background:var(--dark);color:#fff}.labgrid{display:grid;grid-template-columns:minmax(0,1fr) 280px;gap:17px;align-items:start}.workspace{min-width:0;border:1px solid var(--line);border-radius:14px;background:#fff;overflow:hidden}.workhead{background:#20283b;color:#b5c0d8;padding:13px 19px;display:flex;justify-content:space-between;font-size:11px;font-weight:800;letter-spacing:1px}.workspace #labCanvas{width:100%;display:block;touch-action:none;background:#161d30;cursor:grab;user-select:none;-webkit-user-select:none}.workspace #labCanvas:active{cursor:grabbing}.playbar{padding:11px 14px;border-bottom:1px solid var(--line)}.playbar label{margin-left:auto}.playbar input,.toolbar input[type=number]{width:58px;padding:7px;border:1px solid var(--line);border-radius:7px}.panelheading{display:flex;justify-content:space-between;gap:12px;align-items:center;padding:15px 17px 8px;font-size:11px}.panelheading span{color:var(--sub);font-size:11px}.strip{display:flex;gap:7px;overflow-x:auto;padding:8px 16px 15px;scrollbar-width:thin}.frameitem{min-width:65px;border:2px solid var(--line);border-radius:9px;background:#f8fafc;padding:6px 4px;text-align:center;color:var(--sub);font-size:10px}.frameitem.active{border-color:var(--accent);background:var(--soft);color:var(--accent)}.frameitem canvas{width:100%;display:block}.toolbar{padding:12px 15px;border-top:1px solid var(--line);gap:9px}.toolbar label{display:flex;align-items:center;gap:7px;font-size:12px;color:var(--sub)}.toolbar select{border:1px solid var(--line);border-radius:7px;padding:7px;background:white}.sidepanel{padding:22px}.sidepanel h3{margin:0 0 9px}.sidepanel>label{display:block;font-size:12px;font-weight:750;margin:20px 0}.sidepanel label output{float:right;color:var(--accent)}.sidepanel input[type=range],.sidepanel select{display:block;width:100%;margin-top:10px}.sidepanel select{padding:9px;border:1px solid var(--line);border-radius:8px}.sidepanel hr{border:0;border-top:1px solid var(--line);margin:22px 0}.note{font-size:12px;line-height:1.6}.timeline{padding:8px 14px 15px;overflow-x:auto}.ruler{margin-left:160px;height:35px;position:relative;background:#f1f5f9;border-radius:5px;cursor:pointer}.tick{position:absolute;top:10px;font-size:10px;color:var(--sub);transform:translateX(-50%)}.tick:before{content:'';position:absolute;top:-10px;height:7px;width:1px;background:#94a3b8;left:50%}.timelineRow{display:flex;align-items:center;min-height:40px;border-bottom:1px solid var(--line)}.layername{width:160px;flex:none;font-size:11px;color:var(--sub)}.keytrack{flex:1;height:34px;background:#f8fafc;position:relative;cursor:pointer}.keydot{position:absolute;top:10px;transform:translateX(-50%);border:0;background:transparent;color:var(--accent);font-size:17px;padding:0;line-height:16px}.playhead{position:absolute;top:0;bottom:0;width:2px;background:#f97316;pointer-events:none}.graphbox{margin:10px 15px 15px;border:1px solid var(--line);border-radius:10px;overflow:hidden}.graphbox canvas{width:100%;display:block;touch-action:none}.graphbox .toolbar{border-top:1px solid var(--line)}.graphbox .toolbar input[type=range]{width:90px}.graphbox p{padding:0 14px}.quizbox{max-width:790px;padding:28px}.questionmeta{font-size:12px;color:var(--accent);font-weight:800}.question{font-size:23px;line-height:1.35;margin:12px 0 24px}.option{display:block;width:100%;text-align:left;background:white;border:1px solid var(--line);padding:16px;border-radius:10px;margin:9px 0}.option:hover{border-color:var(--accent)}.option.correct{background:#e9f9f1;border-color:#17a773}.option.wrong{background:#fff0ef;border-color:#e55d5d}.feedback{margin:16px 0;padding:15px;border-radius:10px;background:#f1f5f9;line-height:1.6}footer{padding:28px max(24px,calc((100vw - 1250px)/2));border-top:1px solid var(--line);display:flex;justify-content:space-between;gap:18px;align-items:center;font-size:12px;color:var(--sub)}footer strong{font-size:19px;color:var(--ink)}footer p{margin:5px 0}@media(max-width:900px){.hero{grid-template-columns:1fr;gap:20px;padding-top:15px}.heroart{max-width:650px}.learnlayout{grid-template-columns:1fr}.principlelist{display:flex;overflow-x:auto;padding-bottom:8px}.principlelist button{width:190px;flex:none}.labgrid{grid-template-columns:1fr}.sidepanel{display:grid;grid-template-columns:1fr 1fr;gap:0 20px}.sidepanel>h3,.sidepanel>p,.sidepanel>hr,.sidepanel>#exportGif,.sidepanel>#exportStatus,.sidepanel>#downloadLink{grid-column:1/-1}}@media(max-width:600px){.topbar{padding:10px 12px;gap:7px;flex-wrap:wrap}.brand{font-size:17px}.nav{order:3;width:100%;justify-content:space-between;gap:0}.nav a{font-size:11px;padding:9px 8px}.page{padding:30px 14px 55px}.hero h1{letter-spacing:-1.4px}.hero p{font-size:15px}.stats{gap:16px}.steps{grid-template-columns:1fr}.detailpanel{padding:16px}.detailhead h2{font-size:23px}.democontrols{gap:7px}.sliderlabel{justify-content:start;width:100%;flex:auto}.labtabs{display:grid;grid-template-columns:1fr 1fr}.tab{padding:12px 8px;font-size:12px}.playbar{gap:5px}.playbar label{margin-left:0}.sidepanel{display:block}.panelheading{display:block}.panelheading span{display:block;margin-top:5px}.ruler{margin-left:112px}.layername{width:112px;font-size:10px}.quizbox{padding:18px}.question{font-size:20px}footer{display:block}}

/* Draggable keyframes */
.keydot{z-index:3;cursor:grab;touch-action:none;user-select:none;-webkit-user-select:none;transition:color .12s,transform .12s}.keydot:hover,.keydot:focus-visible{color:#f97316;transform:translateX(-50%) scale(1.25);outline:none}.keydot:active,.keydot.dragging{cursor:grabbing;color:#f97316;transform:translateX(-50%) scale(1.35)}.keytrack{touch-action:pan-y}.timeline .ruler{touch-action:pan-y}

/* Numeric property controls: direct value entry beside each slider */
.property-inputs{display:grid;grid-template-columns:minmax(0,1fr) 76px;align-items:center;gap:10px;margin-top:9px}
.sidepanel .property-inputs input[type=range]{display:block;width:100%;margin:0}
.sidepanel .property-inputs .number-input{width:76px;min-width:0;padding:8px 7px;border:1px solid var(--line);border-radius:8px;background:#fff;color:var(--ink);font:600 13px system-ui;text-align:right}
.sidepanel .property-inputs .number-input:focus{outline:2px solid #8a7cff;outline-offset:1px;border-color:var(--accent)}
.sidepanel .property-inputs .number-input:disabled{background:#f1f5f9;color:#94a3b8}
.keytrack{min-width:260px}
.timeline{overflow-x:auto}
@media(max-width:600px){.property-inputs{grid-template-columns:minmax(0,1fr) 72px;gap:8px}.sidepanel .property-inputs .number-input{width:72px}.timeline{padding-left:9px;padding-right:9px}.ruler,.timelineRow{min-width:480px}}

/* Playhead head: draggable time marker inspired by animation timelines */
.timeline .ruler{overflow:visible;touch-action:none}
.playhead-head{position:absolute;top:-2px;z-index:8;transform:translateX(-50%);width:20px;height:22px;padding:0;border:0;border-radius:5px 5px 8px 8px;background:#f97316;color:#fff;font-size:13px;font-weight:900;line-height:20px;text-align:center;cursor:ew-resize;touch-action:none;user-select:none;-webkit-user-select:none;box-shadow:0 2px 6px #f9731640}
.playhead-head:hover,.playhead-head:focus-visible{background:#ea580c;outline:2px solid #fed7aa;outline-offset:2px}
.playhead-head.dragging{background:#c2410c;transform:translateX(-50%) scale(1.12);cursor:grabbing}
.timeline .playhead{z-index:2}

/* Duration controls: synchronized total-frame and seconds inputs */
.playbar label{display:inline-flex;align-items:center;gap:6px;margin:4px 8px 4px 0;font-size:11px;color:var(--sub)}
.playbar input[type=number]{width:68px;min-width:0}
.duration-hint{font-size:11px;color:var(--sub);font-weight:600}
@media(max-width:600px){.playbar label{margin:4px 5px 4px 0}.playbar input[type=number]{width:62px}.duration-hint{display:block;width:100%}}

/* Student name overlay input for both laboratory modes and GIF export */
.playbar .student-name-control{display:inline-flex;align-items:center;gap:7px;margin:4px 8px 4px 0;font-size:11px;color:var(--sub)}
.playbar .student-name-control input{width:150px;max-width:42vw;padding:7px 9px;border:1px solid var(--line);border-radius:7px;background:#fff;color:var(--ink);font:600 12px system-ui}
.playbar .student-name-control input:focus{outline:2px solid #8a7cff;outline-offset:1px}
@media(max-width:600px){.playbar .student-name-control{width:100%;margin:7px 0}.playbar .student-name-control input{flex:1;width:auto;max-width:none;min-width:0}}

/* Timeline ruler, zoom and horizontal navigation controls */
.timeline-tools{display:flex;align-items:center;gap:7px;padding:0 14px 10px;flex-wrap:wrap}
.timeline-tools-label{font-size:11px;font-weight:750;color:var(--sub);margin-right:4px}
.timeline-toolbtn{display:inline-grid;place-items:center;min-width:31px;height:29px;padding:0 8px;border:1px solid var(--line);border-radius:7px;background:#fff;color:#344054;font-size:17px;font-weight:750;line-height:1}
.timeline-toolbtn:hover{border-color:var(--accent);color:var(--accent);background:var(--soft)}
.zoom-readout{min-width:43px;text-align:center;font-size:11px;font-weight:750;color:var(--sub);font-variant-numeric:tabular-nums}
.timeline-tool-separator{height:20px;border-left:1px solid var(--line);margin:0 4px}
.horizontal-scroll-icon{font-size:19px;line-height:1;color:var(--accent);font-weight:800}
.timeline{padding:8px 14px 15px;overflow-x:auto;overscroll-behavior-x:contain;scrollbar-width:thin;scrollbar-color:#aab4c5 #eef2f7}
.timeline-inner{min-width:100%;}
.timeline-inner .ruler{width:calc(100% - 160px);}
.timeline-inner .timelineRow{width:100%;}
.timeline-inner .keytrack{min-width:0;}
.timeline .tick{font-size:9px;font-variant-numeric:tabular-nums;white-space:nowrap}
.timeline .tick.first{transform:none}
.timeline .tick.last{transform:translateX(-100%)}
@media(max-width:600px){.timeline-tools{padding-left:10px;padding-right:10px}.timeline-tools-label{width:100%}.timeline-toolbtn{min-width:34px;height:32px}.timeline{padding-left:10px;padding-right:10px}}


/* v12: Freeze layer labels while the ruler and keyframe tracks scroll horizontally.
   Keeping the keyframe tracks in the same scrolling plane as the ruler preserves alignment. */
.timelineRow .layername{
  position:sticky;
  left:0;
  z-index:6;
  align-self:stretch;
  display:flex;
  align-items:center;
  flex:0 0 160px;
  width:160px;
  min-width:160px;
  padding-right:8px;
  background:#fff;
  box-shadow:3px 0 7px rgba(15,23,42,.08);
  white-space:nowrap;
}
@media(max-width:600px){
  .timelineRow .layername{
    flex-basis:112px;
    width:112px;
    min-width:112px;
    padding-right:5px;
  }
}


/* v13: Student name input is placed above the ball properties in the side panel. */
.sidepanel .sidepanel-student-name{
  display:block;
  grid-column:1/-1;
  margin:0 0 22px;
  padding:12px;
  border:1px solid var(--line);
  border-radius:10px;
  background:#f8fafc;
  color:var(--ink);
  font-size:12px;
  font-weight:750;
}
.sidepanel .sidepanel-student-name input{
  display:block;
  width:100%;
  margin-top:8px;
  padding:10px 11px;
  border:1px solid var(--line);
  border-radius:8px;
  background:#fff;
  color:var(--ink);
}