:root{--blue:#38b6ff;--orange:#ff914d;--ink:#142c43;--muted:#526e84;--line:#dce7ef;--surface:#f3f7fb;font-family:Inter,ui-sans-serif,system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;color:var(--ink);background:var(--surface);font-synthesis:none}*{box-sizing:border-box}body{margin:0}button,input,select{font:inherit}button,select{cursor:pointer}button{border:1px solid var(--line);border-radius:10px;padding:10px 14px;background:white;color:var(--ink);font-size:.85rem;transition:background .15s,border-color .15s,box-shadow .15s}button:hover{background:#eaf6ff;border-color:#9cd8fa}button:disabled{opacity:.4;cursor:default}button:focus-visible,input:focus-visible,select:focus-visible{outline:3px solid var(--blue);outline-offset:3px}button[hidden],div[hidden]{display:none!important}
header{height:96px;display:flex;align-items:center;gap:32px;padding:12px 28px;background:#fff;border-bottom:1px solid var(--line);position:relative}header:after{content:"";position:absolute;bottom:-1px;left:28px;width:88px;height:3px;background:linear-gradient(90deg,var(--orange) 50%,var(--blue) 50%)}.brand{display:flex;align-items:center;gap:14px;font-size:1rem;font-weight:850;letter-spacing:.08em;flex-shrink:0}.brand-logo{display:block;width:64px;height:64px;border-radius:12px;object-fit:contain}.subbrand{display:block;font-size:.69rem;color:var(--muted);letter-spacing:.18em;margin-top:5px;font-weight:650}.chapter{font-size:.65rem;font-weight:750;color:#53738b;letter-spacing:.14em;border-left:1px solid var(--line);padding-left:28px}.chapter b{display:block;color:var(--ink);font-size:.9rem;letter-spacing:0;font-weight:650;margin-top:5px}.language-control{display:flex;align-items:center;gap:9px;font-size:.75rem;color:var(--muted);margin-left:auto}.language-control select{background:#f5f9fc;color:var(--ink);border:1px solid var(--line);border-radius:10px;padding:10px 30px 10px 12px}
main{display:grid;grid-template-columns:270px minmax(320px,1fr) 304px;gap:16px;padding:18px;max-width:1920px;margin:0 auto;height:calc(100dvh - 96px);min-height:600px}aside,.workspace{background:white;border:1px solid var(--line);border-radius:18px;min-width:0}aside{padding:23px 20px;overflow:auto;scrollbar-width:thin;scrollbar-color:#c2d8e6 transparent}main>aside:first-child{display:flex;flex-direction:column}.section-label{font-size:.64rem;letter-spacing:.14em;font-weight:800;color:#53738b}h1{font-size:1.8rem;line-height:1.13;letter-spacing:-.055em;margin:13px 0;color:var(--ink)}h1:after{content:"";display:block;width:35px;height:4px;border-radius:4px;background:var(--orange);margin-top:16px}h2{font-size:1.22rem;line-height:1.3;letter-spacing:-.025em;margin:8px 0}.intro{font-size:.83rem;line-height:1.65;color:var(--muted);margin:0}.tabs{display:flex;flex-direction:column;gap:5px;padding:5px;background:#f3f7fa;border:1px solid #e8eff5;border-radius:12px;margin-top:20px}.tabs button{width:100%;text-align:left;border:0;background:transparent;font-weight:650;padding:10px 11px;font-size:.8rem}.tabs button.active{background:var(--ink);color:white;box-shadow:0 3px 8px #142c4318}.notice{font-size:.74rem;line-height:1.6;border-left:3px solid var(--blue);background:#f0f9ff;padding:9px 11px;margin:17px 0;color:#43677f;border-radius:0 8px 8px 0}
nav{display:flex;flex-direction:column;gap:4px;min-height:120px;overflow:auto;flex:1;scrollbar-width:thin;scrollbar-color:#c2d8e6 transparent}nav button{display:flex;align-items:center;text-align:left;border:1px solid transparent;background:transparent;border-radius:10px;gap:10px;padding:9px 8px;font-size:.78rem;line-height:1.4;flex-shrink:0}nav button:hover{background:#f1f8fc}nav button.active{background:#eaf7ff;border-color:#aee1ff;color:#12557c}nav .num{display:grid;place-items:center;background:#f2f6f9;border-radius:7px;width:27px;min-width:27px;height:27px;font-size:.67rem;font-weight:700;color:#617d92;font-variant-numeric:tabular-nums}nav button.active .num{background:var(--blue);color:#102d44}nav .label{flex:1}.side-footer{border-top:1px solid var(--line);margin-top:16px;padding-top:12px;font-size:.69rem;line-height:1.7;color:#607b91}
.workspace{display:flex;flex-direction:column;overflow:hidden;background:linear-gradient(145deg,#fcfeff,#edf6fc);box-shadow:0 5px 24px #1c557506}.viewer-head{display:flex;align-items:center;justify-content:space-between;padding:23px 24px 13px;gap:16px;z-index:2}.viewer-head h2{font-size:1.3rem;margin-bottom:0}.viewer-head .section-label{color:#356d8e}.viewer-head #reset{font-size:.75rem;white-space:nowrap;background:#ffffffb8}#viewport{position:relative;flex:1;min-height:290px;overflow:hidden;background:radial-gradient(ellipse at 50% 48%,#fff 12%,#f0f8fd 70%)}#viewport:before{content:"";position:absolute;inset:0;pointer-events:none;background-image:radial-gradient(#a7c4d5 1px,transparent 1px);background-size:24px 24px;opacity:.22}canvas{position:relative;display:block;touch-action:none}.views{position:absolute;top:8px;left:24px;z-index:2;display:flex;gap:3px;background:#ffffffd9;padding:4px;border:1px solid var(--line);border-radius:11px;box-shadow:0 3px 12px #244d7008}.views button{padding:6px 10px;font-size:.74rem;border:0;background:transparent;border-radius:7px}.views button.active{background:var(--ink);color:white}.gesture{position:absolute;bottom:15px;left:12px;right:12px;text-align:center;font-size:.68rem;color:#607b91;pointer-events:none}#load{position:absolute;inset:0;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:14px;z-index:4;background:#f0f8fd}#load span{font-size:.82rem;color:var(--muted)}.loader{height:32px;width:32px;border-radius:50%;border:3px solid #dcecf5;border-top-color:var(--orange);border-right-color:var(--blue);animation:spin 1s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}#pick{position:absolute;bottom:95px;left:20px;right:20px;padding:13px 16px;border-radius:12px;background:#142c43f5;color:white;font-size:.8rem;word-break:break-word;box-shadow:0 8px 24px #142c4320}#pick small{display:block;color:#bfd7e7;margin-top:5px}#model-caption{position:absolute;bottom:40px;left:20px;right:20px;padding:9px 12px;background:#ffffffed;border:1px solid var(--line);border-radius:9px;font-size:.75rem;color:var(--muted);pointer-events:none}
.controlbar{background:white;margin:0 16px 16px;padding:17px 18px;border:1px solid var(--line);border-radius:14px;box-shadow:0 6px 20px #173f5908;z-index:2}.step-line{display:flex;justify-content:space-between;align-items:baseline;gap:12px;font-size:.79rem;font-weight:700}#step-total{color:#607b91;font-size:.73rem;font-weight:500;white-space:nowrap}input[type=range]{width:100%;accent-color:#f0803b;margin:17px 0}.actions{display:flex;gap:7px;align-items:center;flex-wrap:wrap}.actions button{font-size:.76rem;padding:9px 12px}.actions label{font-size:.71rem;margin-left:auto;color:var(--muted);display:flex;align-items:center;gap:5px}input[type=checkbox]{accent-color:#157aad}.primary{background:var(--orange);color:#283542;border-color:var(--orange);font-weight:750;box-shadow:0 3px 8px #ff914d20}.primary:hover{background:#ffa66e;border-color:#ffa66e}
.details{padding:25px 22px}.details>h2{margin-top:12px}.details p{font-size:.83rem;line-height:1.7;color:var(--muted)}.status{font-size:.71rem;border-radius:8px;padding:9px 11px;background:#edf8ff;color:#285c7c;line-height:1.5;border:1px solid #d5edfc}.detail-rule{height:1px;background:var(--line);margin:22px 0}#parts{font-size:.77rem;color:var(--muted);line-height:1.55;max-height:210px;overflow:auto;margin-top:10px;word-break:break-word;scrollbar-width:thin}.part-row{padding:8px 0;border-bottom:1px solid #edf2f6}.tip{background:#fff7ef;border:1px solid #ffe3cc;border-radius:12px;padding:14px;margin:22px 0}.tip b{font-size:.79rem}.tip p{font-size:.75rem;margin:6px 0 0}.wide{width:100%}#instructions{padding-left:21px;color:#43627a;font-size:.81rem;line-height:1.7}#instructions li{padding-left:4px;margin-bottom:11px}#instructions li::marker{color:#1479ad;font-weight:750}#pcb-action{margin-top:13px}#hardware{background:#fff6ed;border:1px solid #ffd4b5;border-radius:12px;margin:17px 0;padding:14px}#hardware b{display:block;font-size:.93rem;color:#703a16}#hardware .usage{margin:8px 0;font-size:.78rem;line-height:1.5}#hardware .bolt-length{height:6px;background:var(--orange);border-radius:3px;margin:12px 0}#hardware .hardware-warning{font-size:.77rem;font-weight:650;line-height:1.6}#power-wiring{margin:14px 0;padding:12px;background:#f2f8fc;border:1px solid #c9e5f4;border-radius:12px}#power-wiring strong{display:block;margin-bottom:10px;font-size:.85rem}#power-wiring img{display:block;width:100%;height:auto;margin:12px 0;border-radius:8px}.wire-red,.wire-black,.wire-unused{padding:7px 9px;margin:5px 0;border-radius:6px;font-size:.78rem;font-weight:700}.wire-red{background:#fff0ee;color:#a21c16;border-left:4px solid #ce2b2b}.wire-black{background:#e3e6ea;color:#15181c;border-left:4px solid #202329}.wire-unused,.power-orientation{font-size:.74rem;color:var(--muted)}
@media(min-width:1600px){main{grid-template-columns:290px minmax(320px,1fr) 330px;gap:20px;padding:22px}.viewer-head{padding:26px 28px 15px}aside{padding:26px}}
@media(max-width:1180px){main{grid-template-columns:240px minmax(300px,1fr);height:auto;min-height:calc(100dvh - 96px)}.workspace{min-height:680px}.details{grid-column:1/-1;display:block}.details .tip{display:none}nav{max-height:340px}.side-footer{margin-top:auto;padding-top:15px}.details #parts{max-height:170px}}
@media(max-width:650px){header{height:80px;padding:10px 15px;gap:12px}.brand{gap:10px;font-size:.84rem}.brand-logo{width:52px;height:52px;border-radius:10px}.subbrand{font-size:.56rem}.chapter{display:none}.language-control>span{display:none}.language-control select{padding:8px 6px;max-width:104px;font-size:.73rem}main{display:flex;flex-direction:column;padding:10px;gap:10px;min-height:0}aside{padding:18px}h1{font-size:1.35rem;margin:9px 0}h1 br{display:initial}h1:after,.intro,.side-footer{display:none}.tabs{margin-top:14px}.tabs button{font-size:.78rem;padding:9px}.notice{margin:12px 0;font-size:.7rem}nav{flex-direction:row;min-height:0;max-height:none;overflow:auto;padding-bottom:3px;flex:none}nav button{white-space:nowrap;font-size:.72rem;max-width:280px}nav .label{overflow:hidden;text-overflow:ellipsis}.workspace{min-height:570px}.viewer-head{padding:18px 16px 10px;gap:10px}.viewer-head h2{font-size:1.06rem}.viewer-head #reset{font-size:.68rem;padding:8px}.views{left:16px}.views button{font-size:.7rem}.controlbar{margin:0 10px 10px;padding:14px}.step-line{font-size:.72rem}.actions label{margin:5px 0 0}.actions button{font-size:.71rem}.gesture{font-size:.63rem}.details{padding:20px}#viewport{min-height:335px}}
@media(prefers-reduced-motion:reduce){*{animation:none!important;transition:none!important}}

/* Student navigation and self-checks */
.nav-phase{border:1px solid #e7eef4;border-radius:10px;overflow:hidden;flex-shrink:0;background:#fbfdff}.nav-phase summary{list-style:none;cursor:pointer;padding:10px 9px;font-size:.75rem;font-weight:750;color:#244b66;display:flex;align-items:center;justify-content:space-between;gap:6px}.nav-phase summary::-webkit-details-marker{display:none}.nav-phase summary:before{content:'›';font-size:1rem;color:#f0803b;transition:transform .15s}.nav-phase[open] summary:before{transform:rotate(90deg)}.nav-phase summary small{font-size:.63rem;font-weight:550;color:#71899b;white-space:nowrap}.nav-phase button{width:100%;padding:7px 8px 7px 16px;font-size:.72rem}.nav-phase button .num{width:24px;min-width:24px;height:24px}.student-start,.student-check{border:1px solid #d8eaf5;background:#f3faff;border-radius:12px;padding:13px 14px;margin:15px 0;color:#244b66}.student-start>b,.student-check>b{font-size:.82rem}.student-start ol{padding-left:19px;margin:8px 0 0;font-size:.74rem;line-height:1.55;color:#526e84}.student-start li{margin:4px 0}.student-check{border-left:3px solid var(--blue)}.student-check>p,.student-check div p{font-size:.75rem;line-height:1.55;margin:6px 0 10px;color:#526e84}.student-check div{border-top:1px solid #dcebf4;padding-top:9px}.student-check div b{font-size:.74rem;color:#9a511f}.student-check div p{margin-bottom:0}.nav-phase button[aria-current=step]{background:#eaf7ff;border-color:#aee1ff;color:#12557c}
@media(max-width:650px){.nav-phase{min-width:260px;max-height:230px;overflow:auto}.nav-phase summary{position:sticky;top:0;background:#fbfdff;z-index:1}.student-start,.student-check{margin:11px 0;padding:11px 12px}.student-start ol{font-size:.72rem}}