/* Authoritative styles for the interactive classroom. */
.study-intro{padding:18px 0;background:linear-gradient(120deg,#eff6ff,#f8fbff);border-bottom:1px solid var(--line)}
.study-intro-inner{display:flex;align-items:center;justify-content:space-between;gap:22px}.study-intro h1{font-size:clamp(27px,3vw,39px);margin:3px 0 2px}.study-intro p{margin:0;color:var(--muted);font-size:14px}
.study-context{display:flex;gap:8px}.study-context button{min-width:145px;padding:9px 12px;text-align:left;border:1px solid var(--line);border-radius:11px;background:var(--paper);color:var(--ink);cursor:pointer}.study-context span,.study-context strong{display:block}.study-context span{font-size:9px;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);font-weight:900}.study-context strong{font-size:12px;margin-top:2px}
.study-layout{display:grid;grid-template-columns:180px minmax(560px,1fr) 290px;min-height:calc(100vh - 260px);background:#f3f7fc;transition:grid-template-columns .28s ease}.study-layout.path-collapsed{grid-template-columns:0 minmax(620px,1fr) 290px}
.lesson-sidebar{min-width:0;padding:18px 14px;border-right:1px solid var(--line);background:var(--paper);overflow:hidden;transition:opacity .18s ease,padding .28s ease}.path-collapsed .lesson-sidebar{opacity:0;padding-left:0;padding-right:0;pointer-events:none}
.lesson-sidebar-title{padding:0 3px 14px;border-bottom:1px solid var(--line)}.lesson-kicker{display:block;font-size:10px;font-weight:900;text-transform:uppercase;letter-spacing:.1em;color:var(--blue)}.lesson-sidebar-title strong{display:block;font-size:15px;margin-top:4px}.lesson-list{display:grid;gap:5px;margin:12px 0}.lesson-item{display:flex;gap:9px;align-items:center;padding:9px 7px;border-radius:10px;color:var(--muted)}.lesson-item>span{width:26px;height:26px;flex:none;display:grid;place-items:center;border-radius:50%;background:var(--soft);font-size:11px;font-weight:900}.lesson-item strong,.lesson-item small{display:block}.lesson-item strong{font-size:11px;line-height:1.2}.lesson-item small{font-size:9px;margin-top:2px}.lesson-item.active{background:#e9f2ff;color:var(--blue)}.lesson-item.active>span{background:var(--blue);color:#fff}.lesson-help{display:grid;gap:7px;margin-top:16px;padding:12px;border:1px solid #d9e5f5;border-radius:13px;background:#f8fbff}.lesson-help>strong{font-size:12px}.lesson-help .button{width:100%;min-height:auto;padding:8px;font-size:10px}
.board-wrap{min-width:0;padding:18px 20px 24px}.board-toolbar{display:flex;align-items:end;justify-content:space-between;gap:12px;margin-bottom:11px}.board-toolbar>div:first-child{display:flex;flex-direction:column;min-width:0}.board-toolbar strong{font-size:17px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}.board-live{font-size:9px;color:#087a5b;text-transform:uppercase;letter-spacing:.09em;font-weight:900}.board-live i{display:inline-block;width:7px;height:7px;border-radius:50%;background:var(--mint);margin-right:5px;box-shadow:0 0 0 4px rgba(47,207,159,.13)}.board-actions{display:flex;gap:6px;flex-wrap:wrap;justify-content:flex-end}.board-action{border:1px solid var(--line);background:var(--paper);color:var(--navy);padding:8px 10px;border-radius:9px;font:850 10px/1.1 var(--font);cursor:pointer}.board-action:hover,.board-action:focus-visible{border-color:var(--blue);color:var(--blue)}.path-toggle{border-color:#b8d2f6;background:#edf5ff;color:var(--blue)}
.board{position:relative;overflow:hidden;min-height:620px;border:1px solid var(--line);border-radius:22px;background:var(--paper);box-shadow:0 18px 48px rgba(7,27,52,.09)}.board::before{content:'';position:absolute;inset:0;background-image:linear-gradient(#e7eef8 1px,transparent 1px),linear-gradient(90deg,#e7eef8 1px,transparent 1px);background-size:28px 28px;opacity:.78}.board-content{position:relative;z-index:1;padding:42px 46px}.board-step{display:flex;align-items:center;justify-content:space-between;gap:16px}.board-step-count{font-size:11px;font-weight:850;color:var(--muted);background:var(--soft);border-radius:999px;padding:5px 9px}.board-content h2{max-width:850px;font-size:clamp(34px,3.2vw,50px);line-height:1.06;color:var(--blue);margin:18px 0}.board-content>p{max-width:820px;font-size:18px;line-height:1.55;color:#3e526d}.equation{font-family:Georgia,serif;font-size:clamp(34px,4vw,56px);line-height:1.25;margin:26px 0;padding:21px;text-align:center;background:rgba(255,255,255,.87);border:1px solid #d9e5f5;border-radius:16px}.board-note{padding:16px 18px;border-left:5px solid var(--sun);border-radius:8px;background:#fff8d7;color:#59440a;font-size:16px}.board-question{margin-top:22px;padding:17px 20px;border:2px solid var(--blue);border-radius:14px;background:#edf5ff}.board-question span,.board-question strong{display:block}.board-question span{font-size:10px;color:var(--blue);font-weight:900;text-transform:uppercase;letter-spacing:.09em;margin-bottom:6px}.board-question strong{font-size:18px;line-height:1.4}
.board-content.is-writing>*{opacity:0;transform:translateY(9px);animation:board-write-in .42s cubic-bezier(.2,.8,.2,1) forwards}.board-content.is-writing>*:nth-child(2){animation-delay:.14s}.board-content.is-writing>*:nth-child(3){animation-delay:.28s}.board-content.is-writing>*:nth-child(4){animation-delay:.45s}.board-content.is-writing>*:nth-child(5){animation-delay:.62s}.board-content.is-writing>*:nth-child(6){animation-delay:.8s}@keyframes board-write-in{to{opacity:1;transform:none}}
.board-empty{position:relative;z-index:1;min-height:620px;padding:35px;display:grid;align-content:center;justify-items:center;text-align:center}.board-empty[hidden]{display:none}.board-empty>span{font-size:48px;color:var(--blue)}.board-empty h2{margin:6px 0}.board-empty p{color:var(--muted)}.board-connection{display:flex;align-items:center;justify-content:center;gap:10px;margin-top:13px;color:var(--muted)}.board-connection>span{width:25px;height:25px;display:grid;place-items:center;border-radius:50%;background:var(--blue);color:#fff;font-size:10px;font-weight:900}.board-connection strong,.board-connection small{display:block}.board-connection strong{font-size:11px;color:var(--ink)}.board-connection small{font-size:9px}.board-connection>b{color:#8aa0bb;margin:0 6px}
.class-controls{height:max-content;max-height:calc(100vh - 190px);margin:18px 16px 18px 0;position:sticky;top:130px;align-self:start;border:1px solid var(--line);border-radius:20px;background:var(--paper);box-shadow:0 18px 42px rgba(7,27,52,.11);overflow-y:auto;overscroll-behavior:contain}.teacher-presence{display:flex;gap:10px;align-items:center;padding:16px;border-bottom:1px solid var(--line);background:linear-gradient(135deg,#f8fbff,#edf5ff)}.teacher-avatar{width:42px;height:42px;display:grid;place-items:center;flex:none;border-radius:13px;background:var(--navy);color:#fff;font-size:18px;font-weight:950}.teacher-online{display:block;font-size:9px;text-transform:uppercase;letter-spacing:.1em;color:#087a5b;font-weight:900}.teacher-online i{display:inline-block;width:7px;height:7px;border-radius:50%;background:var(--mint);margin-right:4px}.teacher-presence h3{font-size:16px;margin:2px 0 0}.teacher-presence p{font-size:10px;color:var(--muted);margin:2px 0 0}
.class-start{padding:14px;border-bottom:1px solid var(--line);text-align:center}.start-class{width:100%;min-height:52px;border:0;border-radius:12px;background:var(--blue);color:#fff;font:900 15px/1 var(--font);cursor:pointer;box-shadow:0 9px 20px rgba(13,95,211,.22)}.start-class:hover{transform:translateY(-1px)}.start-class[hidden]{display:none}.class-start p{margin:9px 2px 0;color:var(--muted);font-size:10px;line-height:1.4}.class-start p[data-state=speaking],.class-start p[data-state=working]{color:var(--blue);font-weight:800}.class-start p[data-state=ready]{color:#087a5b;font-weight:800}
.response-panel{padding:15px}.response-panel>label{display:block;font-size:16px;font-weight:950}.response-panel>p{margin:3px 0 11px;color:var(--muted);font-size:11px;line-height:1.4}.quick-replies{display:flex;flex-wrap:wrap;gap:6px;margin:0 0 11px}.quick-replies>span{flex-basis:100%;font-size:9px;font-weight:900;letter-spacing:.1em;text-transform:uppercase;color:#7a5a16}.quick-replies button{border:1px solid #edc55d;background:#fff9df;color:#493200;border-radius:9px;padding:8px 9px;font:800 10px/1.25 var(--font);cursor:pointer;text-align:left}.quick-replies button:hover,.quick-replies button:focus-visible{background:#ffeaa8;border-color:#ca9200}.chat-form{display:grid;grid-template-columns:minmax(0,1fr) 67px;gap:5px;margin:0;padding:5px;border:2px solid var(--blue);border-radius:13px;background:#f4f8ff;box-shadow:0 0 0 4px rgba(13,95,211,.08)}.chat-form:focus-within{box-shadow:0 0 0 5px rgba(13,95,211,.16)}.chat-form textarea{min-width:0;min-height:72px;max-height:130px;padding:8px;border:0;outline:0;resize:vertical;background:transparent;color:var(--ink);font:500 12px/1.4 var(--font)}.send-btn{border:0;border-radius:9px;background:var(--blue);color:#fff;font:900 11px/1 var(--font);cursor:pointer;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:4px}.send-btn:disabled{opacity:.65;cursor:wait}.send-btn b{font-size:14px}
.voice-bar{display:flex;align-items:center;gap:8px;margin-top:10px;padding:9px;border-radius:11px;background:var(--navy);color:#fff}.voice-bar>button{width:34px;height:34px;flex:none;border:0;border-radius:50%;background:var(--blue);color:#fff;cursor:pointer}.voice-bar>button.listening{background:#d92d42;animation:voice-pulse 1s infinite}@keyframes voice-pulse{50%{box-shadow:0 0 0 7px rgba(217,45,66,.25)}}.voice-copy{min-width:0}.voice-copy strong{display:block;font-size:11px}.voice-status{font-size:9px;color:#bad0e8;line-height:1.25}.voice-choice{display:flex;align-items:center;justify-content:space-between;gap:8px;margin-top:9px;color:var(--muted);font-size:9px;font-weight:800}.voice-choice select{max-width:165px;border:1px solid var(--line);border-radius:7px;background:#fff;color:var(--navy);padding:5px;font-size:9px}.mobile-answer-jump{display:none}
body.dark .study-intro{background:linear-gradient(120deg,#10243e,#0d1d31)}body.dark .study-context button,body.dark .lesson-sidebar,body.dark .class-controls,body.dark .board{background:var(--paper)}body.dark .teacher-presence{background:#10243e}body.dark .chat-form{background:#14263d}body.dark .equation{background:rgba(7,27,52,.76)}body.dark .board-note{background:#4c3b08;color:#ffeeb0}body.dark .board-question{background:#102b50}body.dark .quick-replies>span{color:#ffd974}body.dark .quick-replies button{background:#1c2a40;color:#fff1b9;border-color:#755a1d}
@media(max-width:1180px){.study-layout,.study-layout.path-collapsed{grid-template-columns:155px minmax(0,1fr) 260px}.board-wrap{padding-left:14px;padding-right:14px}.board-content{padding:34px 30px}.board{min-height:590px}.class-controls{margin-right:10px}}
@media(max-width:900px){.study-layout,.study-layout.path-collapsed{grid-template-columns:minmax(0,1fr) 280px}.lesson-sidebar{display:none}.path-toggle{display:none}.board{min-height:550px}.board-empty{min-height:550px}.class-controls{top:110px}}
@media(max-width:700px){.study-intro{padding:15px 0}.study-intro-inner{display:block}.study-intro h1{font-size:27px}.study-intro p{font-size:12px}.study-context{margin-top:11px}.study-context button{min-width:0;flex:1;padding:8px 9px}.study-layout,.study-layout.path-collapsed{display:flex;flex-direction:column}.board-wrap{order:1;width:100%;padding:12px}.board-toolbar{align-items:flex-start}.board-actions{gap:5px}.board-action{padding:7px 8px}.board{min-height:510px}.board-content{padding:27px 20px}.board-content h2{font-size:30px}.board-content>p{font-size:15px}.equation{font-size:31px;margin:22px 0;padding:16px 10px}.board-question strong{font-size:15px}.board-empty{min-height:510px}.board-connection{display:none}.class-controls{order:2;width:calc(100% - 24px);max-height:none;margin:0 12px 18px;position:relative;top:auto;overflow:visible}.mobile-answer-jump{display:block;width:100%;margin-top:12px;padding:10px;border:0;border-radius:9px;background:var(--blue);color:#fff;font-weight:900;cursor:pointer}.voice-choice select{max-width:190px}}
@media(prefers-reduced-motion:reduce){.board-content.is-writing>*{opacity:1;transform:none;animation:none}.voice-bar>button.listening{animation:none}}

/* Classroom v4: teacher-led lesson, dominant animated whiteboard */
.classroom-v4{grid-template-columns:210px minmax(0,1fr) 300px;min-height:calc(100vh - 238px);background:#f3f7fd}
.classroom-v4{position:relative}
.classroom-v4.path-collapsed{grid-template-columns:0 minmax(0,1fr) 300px}
.classroom-v4 .lesson-sidebar{width:auto;min-width:0;padding:18px 14px;background:#fff}
.classroom-v4.path-collapsed .lesson-sidebar{display:block;visibility:hidden;padding:0;border:0}
.classroom-v4 .board-wrap{padding:18px 16px 24px}
.classroom-v4 .board{min-height:650px;border-radius:18px}
.classroom-v4 .board-content{min-height:650px;padding:44px 54px 80px}
.classroom-v4 .board-content h2{font-size:clamp(38px,3.2vw,58px);max-width:900px;margin:22px 0 14px}
.classroom-v4 .board-content>p{font-size:18px;max-width:900px}
.classroom-v4 .equation{white-space:pre-line;font-size:clamp(38px,4vw,64px);line-height:1.42;text-align:left;padding:25px 30px;margin:28px 0;background:rgba(255,255,255,.9)}
.board-phase{padding:7px 12px;border-radius:999px;background:#e7f8f2;color:#087a5b;font-size:10px;font-weight:900;text-transform:uppercase;letter-spacing:.08em}
.board-continue{display:flex;justify-content:flex-end;margin-top:24px}
.board-continue[hidden]{display:none}
.board-continue button{border:0;border-radius:12px;background:var(--blue);color:#fff;padding:15px 20px;font:900 14px/1 var(--font);cursor:pointer;box-shadow:0 10px 22px rgba(13,95,211,.2)}
.board-continue button:hover{transform:translateY(-1px)}
.board-continue button span{margin-left:10px}
.board-pen{position:absolute;z-index:5;left:48px;top:94px;width:116px;height:78px;opacity:0;pointer-events:none;will-change:left,top}.writing-hand{position:absolute;right:0;top:0;width:112px;height:auto;filter:drop-shadow(0 5px 5px rgba(0,0,0,.18));transform:rotate(-4deg)}.board-pen svg{position:absolute;right:77px;top:50px;width:56px;height:20px;overflow:visible}.board-pen path{fill:none;stroke:var(--blue);stroke-width:3;stroke-linecap:round;stroke-dasharray:90;stroke-dashoffset:90;animation:doodle-ink 1.45s ease-in-out infinite}@keyframes doodle-ink{0%{stroke-dashoffset:90;opacity:.15}60%,88%{stroke-dashoffset:0;opacity:.85}100%{stroke-dashoffset:-90;opacity:0}}
.board-content.awaiting-speech .writing-line{opacity:.08;filter:blur(1px)}
.board-content.pen-writing .writing-line{clip-path:inset(0 100% 0 0);opacity:1;filter:none;transform:none;animation:marker-reveal var(--write-duration,2.4s) linear var(--write-delay,0s) forwards}
.board-content.pen-writing .board-pen{opacity:1}
@keyframes marker-reveal{to{clip-path:inset(0 0 0 0)}}
.classroom-v4 .class-controls{max-height:calc(100vh - 155px);top:132px;margin:18px 14px 18px 0;border-radius:18px}
.teacher-tools{display:grid;grid-template-columns:repeat(3,1fr);gap:6px;padding:10px 12px;border-bottom:1px solid var(--line)}
.teacher-tools button{min-height:48px;border:1px solid var(--line);border-radius:10px;background:#fff;color:var(--navy);font:900 12px/1 var(--font);cursor:pointer}
.teacher-tools button span{display:block;margin-top:5px;font-size:9px;color:var(--muted)}
.teacher-tools button:hover,.teacher-tools button.active{border-color:var(--blue);background:#edf5ff;color:var(--blue)}
.classroom-v4 .teacher-avatar{width:74px;height:74px;border-radius:50%;object-fit:cover;object-position:center 24%;background:#dce9f7;box-shadow:0 10px 24px rgba(13,95,211,.24);border:3px solid #fff}
.classroom-v4 .teacher-presence h3{font-size:18px}
.classroom-v4 .response-panel>label{font-size:18px}
.classroom-v4 .chat-form textarea{font-size:13px}
.classroom-v4 .lesson-item{padding:11px 8px}
.classroom-v4 .lesson-item>span{width:30px;height:30px}
.classroom-v4 .lesson-help{margin-top:20px}
.focus-board{border-color:var(--blue);background:var(--blue);color:#fff}
.classroom-focus .site-header,.classroom-focus .study-intro,.classroom-focus .site-footer{display:none}
.classroom-focus .classroom-v4{min-height:100vh}
.classroom-focus .classroom-v4 .class-controls{top:12px;max-height:calc(100vh - 24px)}
.classroom-focus .classroom-v4 .board{min-height:calc(100vh - 115px)}
.classroom-focus .classroom-v4 .board-content{min-height:calc(100vh - 115px)}
.classroom-focus .classroom-v4 .board-toolbar{position:sticky;top:0;z-index:10}
.teacher-audio-loader{display:flex;align-items:center;justify-content:center;gap:10px;padding:10px;border-radius:11px;background:#eef5ff;color:var(--navy);text-align:left;margin-bottom:9px}
.teacher-audio-loader[hidden]{display:none}.teacher-audio-loader strong,.teacher-audio-loader small{display:block}.teacher-audio-loader strong{font-size:10px}.teacher-audio-loader small{font-size:8px;color:var(--muted);margin-top:2px}
.voice-wave{display:flex;align-items:center;gap:3px;height:27px}.voice-wave i{display:block;width:3px;height:9px;border-radius:4px;background:var(--blue);animation:voice-wave 1s ease-in-out infinite}.voice-wave i:nth-child(2){animation-delay:.15s}.voice-wave i:nth-child(3){animation-delay:.3s}.voice-wave i:nth-child(4){animation-delay:.45s}@keyframes voice-wave{50%{height:26px}}
.teacher-transcript{position:fixed;z-index:1000;left:50%;bottom:14px;width:min(680px,calc(100vw - 34px));display:flex;align-items:center;gap:8px;padding:7px 11px;border:1px solid rgba(255,255,255,.25);border-radius:12px;background:rgba(7,27,52,.72);color:#fff;box-shadow:0 10px 32px rgba(2,14,31,.22);backdrop-filter:blur(8px);transform:translate(-50%,16px);opacity:0;transition:opacity .24s ease,transform .24s ease;pointer-events:none}
.teacher-transcript[hidden]{display:none}.teacher-transcript.visible{transform:translate(-50%,0);opacity:1}.teacher-transcript>img{width:32px;height:32px;flex:none;border-radius:50%;object-fit:cover;object-position:center 24%;border:1px solid rgba(255,255,255,.9)}.teacher-transcript>div{min-width:0;flex:1;display:flex;align-items:center;gap:8px;overflow:hidden}.teacher-transcript strong{display:block;flex:none;color:#8bdfff;font-size:8px;letter-spacing:.07em;text-transform:uppercase;white-space:nowrap}.teacher-transcript p{min-width:0;overflow:hidden;white-space:nowrap;margin:0;font-size:12px;line-height:1.25;font-weight:700;scroll-behavior:smooth}.transcript-wave{display:flex;align-items:center;gap:2px;height:20px;flex:none}.transcript-wave i{display:block;width:2px;height:7px;border-radius:4px;background:#54d8ad;animation:voice-wave .72s ease-in-out infinite}.transcript-wave i:nth-child(2){animation-delay:.12s}.transcript-wave i:nth-child(3){animation-delay:.24s}

body.dark .teacher-tools button{background:#10243e;color:#fff}
body.dark .board-phase{background:#123b35;color:#8aefd0}

@media(max-width:1180px){
 .classroom-v4,.classroom-v4.path-collapsed{grid-template-columns:175px minmax(0,1fr) 280px}
 .classroom-v4.path-collapsed{grid-template-columns:0 minmax(0,1fr) 280px}
 .classroom-v4 .board-content{padding:38px 34px 74px}
}
@media(max-width:900px){
 .classroom-v4,.classroom-v4.path-collapsed{grid-template-columns:minmax(0,1fr) 275px}
 .classroom-v4 .lesson-sidebar,.classroom-v4.path-collapsed .lesson-sidebar{display:none}
 .classroom-v4 .board-content{padding:34px 28px 70px}
 .classroom-v4 .board{min-height:590px}
 .classroom-v4 .board-content{min-height:590px}
}
@media(max-width:700px){
 .classroom-v4,.classroom-v4.path-collapsed{display:flex;min-height:0}
 .classroom-v4 .board-wrap{order:1;padding:10px 10px 4px}
 .classroom-v4 .board{min-height:545px}
 .classroom-v4 .board-content{min-height:545px;padding:28px 20px 72px}
 .classroom-v4 .board-content h2{font-size:32px;margin:17px 0 12px}
 .classroom-v4 .equation{font-size:34px;padding:20px 17px;margin:21px 0}
 .classroom-v4 .class-controls{order:2;width:calc(100% - 20px);max-height:none;margin:10px;border-radius:16px}
 .classroom-v4 .teacher-presence{padding:13px}
 .classroom-v4 .teacher-avatar{width:60px;height:60px}
 .classroom-v4 .teacher-tools{padding:9px}
 .classroom-v4 .class-start{padding:12px}
 .classroom-v4 .response-panel{padding:13px}
 .classroom-v4 .board-toolbar{position:sticky;top:0;z-index:8;background:#f3f7fd;padding:5px 0 10px}
 .classroom-focus .classroom-v4 .board{min-height:620px}
 .classroom-focus .classroom-v4 .board-content{min-height:620px}
 .classroom-v4 .board-pen{transform:scale(.82) rotate(-12deg);transform-origin:left center}
 .teacher-transcript{bottom:8px;width:calc(100vw - 18px);gap:6px;padding:6px 8px;border-radius:10px}.teacher-transcript>img{width:28px;height:28px}.teacher-transcript>div{gap:6px}.teacher-transcript p{font-size:11px}.teacher-transcript strong{font-size:7px}.transcript-wave{display:none}
}
@media(prefers-reduced-motion:reduce){
 .board-content.pen-writing .writing-line{clip-path:none;animation:none}
 .board-content.pen-writing .board-pen{display:none}
 .teacher-transcript{transition:none}
}