:root {
    --bg: #0b1120;
    --bg-soft: #111a2e;
    --panel: #16203a;
    --ink: #e8eefc;
    --ink-dim: #9fb0d0;
    --line: #25304d;
    --hot: #ef4444;
    --warm: #f59e0b;
    --cool: #38bdf8;
    --cold: #22d3ee;
    --accent: #38bdf8;
    --shadow: 0 12px 40px rgba(0, 0, 0, 0.45);
    --radius: 18px;
    color-scheme: dark;
    font-family: system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

* { box-sizing: border-box; }

body, html {
    margin: 0;
    padding: 0;
    background:
        radial-gradient(1200px 600px at 80% -10%, #16284d 0%, transparent 60%),
        radial-gradient(1000px 500px at 0% 0%, #102038 0%, transparent 55%),
        var(--bg);
    color: var(--ink);
    line-height: 1.6;
    min-height: 100vh;
}

.hero {
    max-width: 880px;
    margin: 0 auto;
    padding: 64px 24px 24px;
    text-align: center;
}

.kicker {
    text-transform: uppercase;
    letter-spacing: 0.18em;
    font-size: 0.8rem;
    color: var(--cool);
    font-weight: 600;
    margin: 0 0 12px;
}

.hero h1 {
    font-size: clamp(1.9rem, 4.5vw, 3rem);
    line-height: 1.15;
    margin: 0 0 18px;
    letter-spacing: -0.02em;
}

.lede {
    font-size: 1.12rem;
    color: var(--ink-dim);
    max-width: 640px;
    margin: 0 auto;
}
.lede em { color: var(--ink); font-style: normal; font-weight: 600; }

main { max-width: 1100px; margin: 0 auto; padding: 16px 24px 48px; }

/* controls */
.controls {
    display: flex;
    flex-wrap: wrap;
    gap: 24px;
    justify-content: center;
    margin: 8px 0 18px;
}
.control-block { display: flex; flex-direction: column; gap: 6px; align-items: center; }
.control-label {
    font-size: 0.7rem;
    text-transform: uppercase;
    letter-spacing: 0.14em;
    color: var(--ink-dim);
    font-weight: 700;
}
.toggle {
    display: inline-flex;
    background: var(--bg-soft);
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 4px;
    gap: 4px;
    flex-wrap: wrap;
    justify-content: center;
}
.seg {
    background: transparent;
    color: var(--ink-dim);
    border: none;
    border-radius: 9px;
    padding: 8px 14px;
    font-size: 0.92rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.15s, color 0.15s;
    white-space: nowrap;
}
.seg:hover { color: var(--ink); }
.seg.active { background: var(--accent); color: #0b1120; }

.mode-banner {
    text-align: center;
    color: var(--ink);
    background: var(--bg-soft);
    border: 1px solid var(--line);
    border-left: 3px solid var(--accent);
    border-radius: 12px;
    padding: 12px 18px;
    margin: 0 auto 8px;
    max-width: 760px;
    font-size: 0.98rem;
}

.stage {
    display: grid;
    grid-template-columns: 1.4fr 1fr;
    gap: 28px;
    align-items: stretch;
    margin-top: 24px;
}

.diagram-wrap {
    background: var(--bg-soft);
    border: 1px solid var(--line);
    border-radius: var(--radius);
    padding: 12px;
    box-shadow: var(--shadow);
}

#cycle { width: 100%; height: auto; display: block; }

/* zones */
.zone { fill: rgba(255, 255, 255, 0.02); stroke: var(--line); stroke-width: 1.5; stroke-dasharray: 6 7; }
.zone-hot  { fill: rgba(239, 68, 68, 0.06); }
.zone-cold { fill: rgba(56, 189, 248, 0.06); }
.zone-label {
    fill: var(--ink-dim);
    font-size: 14px;
    font-weight: 700;
    letter-spacing: 0.14em;
    text-anchor: middle;
}
.zone-sub {
    fill: var(--ink-dim);
    font-size: 10.5px;
    letter-spacing: 0.04em;
    text-anchor: middle;
    opacity: 0.75;
}

/* pipes */
.pipe { fill: none; stroke-width: 7; stroke-linecap: round; opacity: 0.55; }
.pipe-hot  { stroke: var(--hot); }
.pipe-warm { stroke: var(--warm); }
.pipe-cool { stroke: var(--cool); }
.pipe-cold { stroke: var(--cold); }

.arrow { opacity: 0.85; }
.arrow:nth-of-type(1) { fill: var(--hot); }
/* arrows colored individually below via fill in markup order */
.arrow { fill: var(--ink-dim); }

.dot { filter: drop-shadow(0 0 6px currentColor); }
.dot-hot  { fill: var(--hot);  color: var(--hot); }
.dot-warm { fill: var(--warm); color: var(--warm); }
.dot-cool { fill: var(--cool); color: var(--cool); }
.dot-cold { fill: var(--cold); color: var(--cold); }

/* nodes */
.node { cursor: pointer; outline: none; }
.node rect {
    fill: var(--panel);
    stroke: var(--line);
    stroke-width: 2;
    transition: stroke 0.18s, fill 0.18s, transform 0.18s;
}
.node:hover rect, .node:focus-visible rect { stroke: var(--accent); fill: #1b2747; }
.node.active rect { stroke: var(--accent); stroke-width: 3; fill: #1d2c52; }
.node-badge {
    fill: rgba(56, 189, 248, 0.16);
    stroke: var(--accent);
    stroke-width: 1.5;
    transition: fill 0.18s;
}
.node.active .node-badge { fill: var(--accent); }
.node-num {
    fill: var(--ink);
    font-size: 14px;
    font-weight: 800;
    text-anchor: middle;
}
.node.active .node-num { fill: #0b1120; }
.node-title { fill: #ffffff; font-size: 16px; font-weight: 700; text-anchor: middle; }
.node-sub { fill: var(--ink-dim); font-size: 11px; letter-spacing: 0.1em; text-anchor: middle; text-transform: uppercase; }
.node-loc { fill: var(--accent); font-size: 12px; font-weight: 700; text-anchor: middle; opacity: 0.95; }

/* info panel */
.panel {
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: var(--radius);
    padding: 26px;
    box-shadow: var(--shadow);
    min-height: 100%;
}
.panel-empty { color: var(--ink-dim); }
.panel-hint { font-size: 1.2rem; color: var(--ink); font-weight: 700; margin: 0 0 8px; }

.panel-card { animation: fade 0.25s ease; }
@keyframes fade { from { opacity: 0; transform: translateY(8px); } to { opacity: 1; transform: none; } }

.badge {
    display: inline-block;
    font-size: 0.72rem;
    text-transform: uppercase;
    letter-spacing: 0.12em;
    font-weight: 700;
    padding: 4px 10px;
    border-radius: 999px;
    color: #0b1120;
    margin-bottom: 12px;
}
.panel-card h2 { margin: 0 0 4px; font-size: 1.6rem; }
.panel-card .component { color: var(--ink-dim); margin: 0 0 18px; font-weight: 600; }
.panel-card p.detail { color: var(--ink); }

.facts {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 10px;
    margin: 18px 0;
}
.fact {
    background: var(--bg-soft);
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 10px 12px;
}
.fact .k { font-size: 0.68rem; text-transform: uppercase; letter-spacing: 0.1em; color: var(--ink-dim); display: block; }
.fact .v { font-weight: 700; font-size: 0.98rem; }

.flow {
    display: flex;
    align-items: center;
    gap: 8px;
    background: var(--bg-soft);
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 12px;
    margin: 14px 0;
    font-size: 0.92rem;
}
.flow .arrow-i { color: var(--accent); font-weight: 800; }

.home-note {
    border-left: 3px solid var(--accent);
    padding: 8px 0 8px 14px;
    margin: 18px 0 0;
    color: var(--ink-dim);
    font-style: italic;
}
.home-note strong { color: var(--ink); font-style: normal; }

.panel-nav { display: flex; justify-content: space-between; margin-top: 22px; gap: 10px; }
.panel-nav button {
    flex: 1;
    background: var(--bg-soft);
    color: var(--ink);
    border: 1px solid var(--line);
    border-radius: 10px;
    padding: 10px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: border-color 0.15s, background 0.15s;
}
.panel-nav button:hover { border-color: var(--accent); background: #1b2747; }

.prose { max-width: 760px; margin: 56px auto 0; padding: 0 4px; }
.prose h2 { font-size: 1.5rem; }
.prose p { color: var(--ink-dim); }
.prose strong { color: var(--ink); }

/* refrigerant card */
.ref-section { margin-top: 26px; }
.ref-card {
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: var(--radius);
    padding: 24px;
    box-shadow: var(--shadow);
}
.ref-head { border-left: 4px solid var(--accent); padding-left: 14px; }
.ref-head h3 { margin: 0 0 4px; font-size: 1.5rem; }
.ref-alt { color: var(--ink-dim); font-size: 1rem; font-weight: 500; }
.ref-use { margin: 0; color: var(--ink-dim); }
.ref-note { color: var(--ink); margin: 16px 0; }
.ref-stats {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
    gap: 12px;
}
.rstat {
    background: var(--bg-soft);
    border: 1px solid var(--line);
    border-radius: 12px;
    padding: 12px 14px;
}
.rstat .k { display: block; font-size: 0.7rem; text-transform: uppercase; letter-spacing: 0.08em; color: var(--ink-dim); margin-bottom: 4px; }
.rstat .v { font-weight: 700; font-size: 1.02rem; }
.gwp-zero { color: var(--cold); }

/* fans */
.fans-section { margin-top: 56px; }
.fans-section h2 { font-size: 1.6rem; margin-bottom: 6px; }
.fans-intro { color: var(--ink-dim); max-width: 720px; margin-top: 0; }
.fans-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
    gap: 16px;
    margin-top: 20px;
}
.fan {
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: 14px;
    padding: 20px;
}
.fan-head { display: flex; align-items: center; gap: 14px; margin-bottom: 12px; }
.fan-icon { font-size: 1.9rem; }
.fan-name { margin: 0; font-size: 1.2rem; }
.fan-meta { margin: 2px 0 0; color: var(--ink-dim); font-size: 0.85rem; }
.fan-job { color: var(--ink); font-weight: 600; margin: 0 0 10px; }
.fan-detail { color: var(--ink-dim); margin: 0; font-size: 0.94rem; line-height: 1.6; }

/* faults */
.faults-section { margin-top: 56px; }
.faults-section h2 { font-size: 1.6rem; margin-bottom: 6px; }
.faults-intro { color: var(--ink-dim); max-width: 720px; margin-top: 0; }
.faults-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(260px, 1fr));
    align-items: start;
    gap: 14px;
    margin-top: 20px;
}
.fault {
    text-align: left;
    background: var(--panel);
    border: 1px solid var(--line);
    border-radius: 14px;
    padding: 0;
    cursor: pointer;
    overflow: hidden;
    transition: border-color 0.15s, transform 0.15s;
    font: inherit;
    color: inherit;
}
.fault:hover { border-color: var(--accent); transform: translateY(-2px); }
.fault.open { border-color: var(--accent); }
.fault-head {
    display: grid;
    grid-template-columns: auto 1fr auto;
    align-items: center;
    gap: 10px;
    padding: 16px 18px;
}
.fault-icon { font-size: 1.4rem; }
.fault-title { font-weight: 700; font-size: 1.02rem; }
.fault-sev {
    font-size: 0.62rem;
    text-transform: uppercase;
    letter-spacing: 0.06em;
    font-weight: 800;
    padding: 4px 8px;
    border-radius: 999px;
    white-space: nowrap;
}
.sev-diy   { background: rgba(34, 211, 238, 0.16); color: var(--cold); }
.sev-pro   { background: rgba(239, 68, 68, 0.16); color: var(--hot); }
.sev-mixed { background: rgba(245, 158, 11, 0.16); color: var(--warm); }
.fault-body {
    display: none;
    padding: 0 18px 18px;
    border-top: 1px solid var(--line);
    margin-top: -1px;
}
.fault.open .fault-body { display: block; animation: fade 0.2s ease; }
.fdetail { margin: 12px 0 0; color: var(--ink-dim); font-size: 0.92rem; line-height: 1.55; }
.fdetail strong { color: var(--ink); }

/* heat-pump theme: warm up the page when heating */
body.heating { --accent: #f59e0b; }
body.heating .zone-hot  { fill: rgba(239, 68, 68, 0.09); }
body.heating .zone-cold { fill: rgba(56, 189, 248, 0.04); }
body.heating .kicker { color: var(--warm); }

footer {
    text-align: center;
    color: var(--ink-dim);
    padding: 40px 16px;
    font-size: 0.9rem;
    border-top: 1px solid var(--line);
    margin-top: 48px;
}

@media (max-width: 820px) {
    .stage { grid-template-columns: 1fr; }
    .hero { padding-top: 40px; }
}

@media (prefers-reduced-motion: reduce) {
    .dot, .panel-card { animation: none !important; }
}