*{box-sizing:border-box}body{margin:0;background:#f6f5ee;color:#153b31;font:16px/1.5 system-ui,sans-serif}header{max-width:1400px;margin:auto;padding:24px 32px;border-bottom:1px solid #d5ddd5;display:flex;justify-content:space-between;align-items:center}header b{font-size:30px;letter-spacing:-1px}small{display:block;font-size:10px;letter-spacing:1px}a{color:#17674f}header a{font-size:13px}main{max-width:1400px;padding:32px;margin:auto}.intro{display:grid;grid-template-columns:1.3fr 1fr;gap:50px;align-items:center}.eyebrow{font-size:10px;letter-spacing:2px;font-weight:800}h1{font-size:clamp(36px,4vw,58px);line-height:1.08;letter-spacing:-2px;margin:16px 0}em{font-style:normal;color:#217654}.intro p{color:#63746b}.guide{padding:24px;border-left:3px solid #cfa764}.guide span{font-size:12px}.guide p{font-size:14px}button{font:600 13px system-ui;cursor:pointer;border:1px solid #cbd7ce;background:white;border-radius:8px;padding:11px 14px;color:#153b31}button:hover{background:#e4eee4}button:focus-visible{outline:3px solid #d69825;outline-offset:3px}button:disabled{opacity:.4;cursor:default}nav{display:flex;gap:8px;flex-wrap:wrap;margin:28px 0}nav button[aria-pressed=true],.primary{background:#17674f;color:white;border-color:#17674f}.layout{display:grid;grid-template-columns:minmax(0,1fr) 300px;gap:24px;align-items:start}.toolbar{display:flex;justify-content:space-between;gap:10px;align-items:center;margin-bottom:14px}.toolbar strong{font-size:15px}.toolbar button{font-size:12px;padding:8px}#board{position:relative;border:1px solid #cfdbd2;border-radius:16px;background:radial-gradient(#cdd8cf 1px,transparent 1px),#edf1e9;background-size:20px 20px;padding:26px;overflow:hidden}#cables{position:absolute;inset:0;width:100%;height:100%;pointer-events:none;z-index:3}.output{position:relative;display:flex;gap:16px;align-items:center;background:#fff;padding:14px 20px;border-radius:10px;border:1px solid #cbd7ce;min-height:80px}.output>span{flex:1;font-size:12px;font-weight:800}.output small{letter-spacing:0;font-weight:400;margin-top:5px}#batteries{display:grid;grid-template-columns:1fr 1fr;gap:64px 38px;padding:68px 0 22px}.battery{position:relative;border-radius:12px;background:linear-gradient(110deg,#323e40,#17282a);box-shadow:0 9px 0 #111d1e,0 15px 15px #183b3020;padding:40px 18px 20px;color:white;min-height:170px;border-top:14px solid #435356}.battery:after{content:'';position:absolute;top:55px;left:22%;width:56%;height:13px;border:3px solid #617171;border-radius:5px}.battery-label{margin-top:25px;background:#eeeedd;color:#17362e;padding:8px;border-radius:4px;display:flex;justify-content:space-between;gap:4px;align-items:center}.battery-label strong{font-size:23px}.battery-label span{font-size:11px}.terminal{position:relative;z-index:4;width:46px;height:46px;border-radius:50%;padding:0;font-size:26px;color:white;border:4px solid #c8cccc;box-shadow:0 3px 0 #818d8c;flex-shrink:0}.battery .terminal{position:absolute;top:-29px}.battery .minus{left:20px}.battery .plus{right:20px}.minus{background:#1a252c}.plus{background:#c23d3d}.terminal:hover{background:#82773f}.terminal[aria-pressed=true]{outline:5px solid #edb843;outline-offset:4px}#feedback{padding:13px 16px;background:#e4eee3;border-left:3px solid #4a8260;border-radius:5px;min-height:50px;font-size:14px}#feedback.error{background:#f9e6df;border-color:#bb4b3e;color:#873021}.cable-list{margin-top:20px}#wire-list{display:flex;flex-wrap:wrap;gap:6px;margin-top:10px}#wire-list button{font-size:11px;padding:8px}aside{background:#edf1e8;border:1px solid #d3ddd1;border-radius:14px;padding:22px}.readouts{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:20px}.readouts>div{background:#fff;border-radius:8px;padding:13px}.readouts>div:last-child{grid-column:span 2}.readouts strong{display:block;font-size:34px;line-height:1.1;font-variant-numeric:tabular-nums}.readouts span{font-size:9px;letter-spacing:1px}#result{font-size:14px;min-height:60px}aside>button{width:100%;margin:5px 0}#hint-text{font-size:13px;background:#fff5db;padding:14px;border-radius:8px}.learning{border-top:1px solid #cdd9cb;margin-top:20px;padding-top:8px}.learning h3{font-size:13px;margin-bottom:4px}.learning p{font-size:12px;color:#5d7165;margin-top:0}.footnote{font-size:12px;color:#6b786e;margin-top:30px;max-width:1000px}.source{font-size:11px}@media(max-width:900px){.layout{grid-template-columns:1fr}aside{display:block}.readouts{grid-template-columns:repeat(3,1fr)}.readouts>div:last-child{grid-column:auto}.intro{gap:15px}.guide{padding:15px}}@media(max-width:550px){main{padding:20px 14px}header{padding:16px}.intro{grid-template-columns:1fr}.guide{padding:10px 15px}nav button{flex:1;font-size:11px;padding:10px}.toolbar{align-items:start}.toolbar strong{max-width:45%}#board{padding:15px}#batteries{gap:60px 20px;padding-top:65px}.battery{padding:30px 9px 14px;min-height:160px}.battery-label{display:block}.battery .minus{left:5px}.battery .plus{right:5px}.terminal{width:44px;height:44px}.output{padding:12px;gap:9px}.output>span{font-size:10px}.output small{font-size:9px}.battery:after{left:17%;width:66%;top:40px}.readouts strong{font-size:26px}.readouts>div{padding:10px}.readouts span{font-size:8px}}
.primary:hover{background:#12513e;color:white}.battery:after{top:24px}

.busbars{position:relative}.bus-note{font-size:10px;font-weight:800;letter-spacing:1px;margin:0 0 14px}.busbar{display:grid;grid-template-columns:145px 1fr;align-items:center;gap:18px;padding:12px 18px;margin-bottom:14px;border-radius:10px;border:1px solid #c8d2c8;background:#fbfcf7}.bus-label b{font-size:12px}.bus-label small{font-size:9px;margin-top:4px;color:#68796e}.positive .bus-label b{color:#af3030}.bus-strip{display:flex;align-items:center;justify-content:space-between;position:relative;padding:0 8px;isolation:isolate}.bus-strip:before{content:'';position:absolute;left:0;right:0;height:23px;background:linear-gradient(#d6a86b,#b77d45,#deae74);border:1px solid #976536;box-shadow:0 3px 0 #754e34;border-radius:4px;z-index:-1}.bus-strip .terminal{width:42px;height:42px;font-size:22px;border-width:5px;box-shadow:0 2px 0 #666}.bus-help{font-size:11px;letter-spacing:0;color:#607466}#batteries{padding-top:62px}@media(max-width:550px){.busbar{grid-template-columns:1fr;gap:10px;padding:10px 12px}.bus-label{display:flex;align-items:center;justify-content:space-between}.bus-label small{margin:0}.bus-strip .terminal{width:44px;height:44px}.bus-note{font-size:9px;letter-spacing:.5px}}

/* Short-circuit teaching effect: decorative, finite, no flashing loop. */
.fault-effect{position:absolute;inset:0;z-index:8;pointer-events:none;overflow:hidden;border-radius:16px}.fault-haze{position:absolute;inset:0;background:radial-gradient(circle at var(--fault-x) var(--fault-y),#ff8b2655,transparent 65%);animation:fault-glow 3s ease-out forwards}.fault-origin{position:absolute;left:var(--fault-x);top:var(--fault-y)}.fire{position:absolute;bottom:0;left:-25px;width:50px;height:95px;border-radius:80% 15% 65% 40%;background:linear-gradient(0deg,#fff5b1,#ffc42e 35%,#f45818 70%,#b9250b00);filter:drop-shadow(0 0 14px #ff6d16);transform-origin:50% 100%;animation:flame-rise 1.3s ease-in-out 2}.fire-b{width:30px;height:68px;left:-4px;animation-delay:.13s;transform:rotate(20deg)}.fire-c{width:25px;height:52px;left:-35px;animation-delay:.2s;transform:rotate(-20deg)}.smoke{position:absolute;left:-26px;top:-45px;width:62px;height:62px;border-radius:50%;background:radial-gradient(circle,#3a3836aa,#68625c77 55%,transparent 72%);filter:blur(5px);opacity:0;animation:smoke-rise 2.4s ease-out forwards;animation-delay:calc(var(--i)*.08s)}.spark{position:absolute;width:5px;height:16px;background:#ffd85e;border-radius:50%;box-shadow:0 0 7px #fa6b1e;animation:spark-fly .65s ease-out both;animation-delay:var(--delay);transform-origin:0 0}.fault-banner{position:absolute;bottom:16px;left:16px;right:16px;background:#772515f2;color:#fff4d6;border:1px solid #f39552;border-radius:8px;padding:12px 16px;font-size:18px;font-weight:900;letter-spacing:1px;box-shadow:0 8px 25px #32120955}.fault-banner span{display:block;font-size:11px;font-weight:500;letter-spacing:0;margin-top:3px}@keyframes flame-rise{0%{opacity:0;transform:scale(.35) rotate(-10deg)}25%{opacity:1;transform:scale(1) rotate(8deg)}60%{opacity:.9;transform:scale(.85,1.2) rotate(-8deg)}100%{opacity:0;transform:scale(.5,1.4)}}@keyframes smoke-rise{0%{opacity:0;transform:translate(0,0) scale(.4)}20%{opacity:.8}100%{opacity:0;transform:translate(calc((var(--i) - 3)*20px),-185px) scale(2.7)}}@keyframes spark-fly{0%{opacity:1;transform:rotate(var(--angle)) translateY(0)}100%{opacity:0;transform:rotate(var(--angle)) translateY(-115px)}}@keyframes fault-glow{0%{opacity:1}100%{opacity:0}}@media(prefers-reduced-motion:reduce){.fire,.smoke,.spark,.fault-haze{animation:none}.smoke,.spark{display:none}.fire{height:50px}.fault-haze{opacity:.25}}

body{display:flow-root}.course-link{display:flex;justify-content:space-between;align-items:center;gap:18px;padding:18px 20px;margin:20px 0;background:#e6eee3;border:1px solid #cbd9ca;border-radius:10px}.course-link strong{font-size:14px}.course-link p{font-size:12px;margin:4px 0 0;color:#52695b}.course-link a{display:inline-block;background:#17674f;color:white;text-decoration:none;font-size:13px;font-weight:700;border-radius:7px;padding:12px 16px;white-space:nowrap}.course-link a:hover{background:#114e3c}@media(max-width:600px){.course-link{display:block;padding:15px}.course-link a{margin-top:12px;white-space:normal}}