.concept-page { --concept:#7db6c5;background:var(--paper); }
.concept-page main,.concept-page .lesson-header,.concept-page footer { width:min(1060px,calc(100% - 48px));margin-inline:auto; }
.concept-hero { min-height:650px;display:flex;flex-direction:column;justify-content:center;padding:80px 0; }
.concept-hero h1 { max-width:960px;font-size:clamp(62px,9vw,108px); }.concept-hero .lead{max-width:720px;margin-bottom:0}.concept-hero .eyebrow{color:var(--green)}
.concept-section { padding:100px 0;border-top:1px solid var(--line);scroll-margin-top:30px; }
.concept-section h2 { max-width:820px;margin-bottom:28px;font-size:clamp(42px,6vw,68px);line-height:1; }
.concept-section>.lead { max-width:720px; }
.concept-grid { display:grid;grid-template-columns:repeat(3,1fr);gap:16px;margin-top:48px; }
.concept-card { padding:28px;border:1px solid var(--line);background:var(--card); }
.concept-card>span { display:grid;place-items:center;width:48px;height:48px;margin-bottom:45px;border-radius:50%;background:var(--green);color:var(--paper);font:500 21px/1 "DM Mono",monospace; }
.concept-card h3 { margin-bottom:13px;font-size:23px;font-weight:500; }.concept-card p,.concept-prose p { color:var(--muted);font-size:14px;line-height:1.7; }
.concept-prose { display:grid;grid-template-columns:1fr 1fr;gap:48px;margin-top:46px; }
.interactive-panel { margin-top:48px;padding:38px;border:1px solid var(--line);background:var(--card); }
.interactive-panel header { display:flex;justify-content:space-between;gap:20px;margin-bottom:35px; }.interactive-panel h3 { margin:0;font-size:24px;font-weight:500; }.interactive-panel header p { max-width:430px;margin:0;color:var(--muted);font-size:12px;line-height:1.6; }
.control-row { display:grid;grid-template-columns:1fr 1fr;gap:30px;margin-top:28px; }.control-row label { font-size:12px;font-weight:600; }.control-row input[type="range"] { width:100%;margin-top:17px;accent-color:var(--accent); }
.pill-controls { display:flex;flex-wrap:wrap;gap:8px; }.pill-controls button { padding:10px 15px;border:1px solid var(--line);border-radius:22px;background:transparent;cursor:pointer;font:500 9px/1 "DM Mono",monospace;text-transform:uppercase; }.pill-controls button.active{border-color:var(--accent);background:var(--accent);color:white}
.model-stage { min-height:260px;display:grid;place-items:center;position:relative;margin-top:25px;overflow:hidden;background:#e9e4d9; }.model-particles { display:flex;align-items:center;gap:var(--particle-gap,120px); }.model-particle{display:grid;place-items:center;width:88px;height:88px;border-radius:50%;background:var(--green);color:white;font:500 34px/1 "DM Mono",monospace;box-shadow:0 0 0 18px rgb(28 89 73 / 8%)}
.model-arrow { position:absolute;bottom:28px;color:var(--accent);font:500 11px/1 "DM Mono",monospace;text-transform:uppercase; }
.takeaway { display:grid;grid-template-columns:150px 1fr;gap:30px;margin-top:35px;padding:25px;border-left:3px solid var(--concept);background:rgb(125 182 197 / 12%); }.takeaway strong{font-size:13px}.takeaway p{margin:0;color:var(--muted);font-size:13px;line-height:1.65}
.energy-flow { display:grid;grid-template-columns:repeat(4,1fr);margin-top:48px;border:1px solid var(--line); }.energy-step { min-height:220px;padding:24px;border-right:1px solid var(--line);background:var(--card);cursor:pointer; }.energy-step:last-child{border:0}.energy-step.active{background:var(--green);color:white}.energy-step span{font:500 9px/1 "DM Mono",monospace;color:var(--accent)}.energy-step h3{margin:55px 0 12px;font-size:19px;font-weight:500}.energy-step p{margin:0;color:var(--muted);font-size:12px;line-height:1.55}.energy-step.active p{color:rgb(255 255 255 / 65%)}
.energy-detail{padding:28px;background:#e9e4d9;color:var(--muted);font-size:14px;line-height:1.7}.energy-calculator{display:grid;grid-template-columns:1fr 1fr;gap:40px;align-items:center;margin-top:48px;padding:36px;background:var(--green);color:white}.energy-calculator label{display:block;margin:20px 0;font-size:12px}.energy-calculator input{width:100%;margin-top:12px;accent-color:var(--accent)}.energy-result output{display:block;margin-bottom:14px;font:500 clamp(38px,6vw,64px)/1 "DM Mono",monospace;color:var(--mint)}.energy-result p{color:rgb(255 255 255 / 65%);line-height:1.6}
.concept-next { padding:80px 0;text-align:center; }.concept-next a { display:inline-block;margin-top:20px;padding:15px 22px;background:var(--ink);color:var(--paper);text-decoration:none;font-size:12px; }
@media(max-width:760px){.concept-page main,.concept-page .lesson-header,.concept-page footer{width:min(100% - 32px,1060px)}.concept-grid,.concept-prose,.control-row,.energy-calculator{grid-template-columns:1fr}.energy-flow{grid-template-columns:1fr 1fr}.energy-step:nth-child(2){border-right:0}.energy-step:nth-child(-n+2){border-bottom:1px solid var(--line)}.interactive-panel{padding:24px}.interactive-panel header{flex-direction:column}.takeaway{grid-template-columns:1fr;gap:10px}}