:root {
    --bg: #f6f7fb;
    --surface: #ffffff;
    --panel: #f8faff;
    --text: #0f172a;
    --muted: #64748b;
    --border: #e3e8f0;
    --border-strong: #cfd7e3;
    --accent: #2563eb;
    --accent-hover: #1d4ed8;
    --accent-soft: #eef3ff;
    --highlight: #f59e0b;
    --error: #b42318;
    --error-soft: #fef3f2;
    --shadow: 0 1px 2px rgb(15 23 42 / .04), 0 4px 16px rgb(15 23 42 / .05);
    --shadow-lg: 0 12px 40px rgb(15 23 42 / .14);
    --radius: 14px;
    --mono: "JetBrains Mono", ui-monospace, SFMono-Regular, Consolas, monospace;
    color-scheme: light;
}

@media (prefers-color-scheme: dark) {
    :root {
        --bg: #0b1020;
        --surface: #121a2c;
        --panel: #0f1626;
        --text: #e6eaf2;
        --muted: #8d98ad;
        --border: #222c42;
        --border-strong: #2e3a54;
        --accent: #6e9bff;
        --accent-hover: #8fb2ff;
        --accent-soft: #18233d;
        --highlight: #fbbf24;
        --error: #ff9b8f;
        --error-soft: #2c1717;
        --shadow: 0 1px 2px rgb(0 0 0 / .3);
        --shadow-lg: 0 12px 40px rgb(0 0 0 / .5);
        color-scheme: dark;
    }
}

* { box-sizing: border-box; }

body {
    margin: 0;
    background: var(--bg);
    color: var(--text);
    font: 16px/1.6 Inter, system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
    -webkit-font-smoothing: antialiased;
}

a { color: var(--accent); text-underline-offset: 3px; }
a:hover { color: var(--accent-hover); }

.wrap { max-width: 1120px; margin: 0 auto; padding: 0 20px; }
.muted { color: var(--muted); }

/* ---------- header ---------- */

.site-header { background: var(--surface); border-bottom: 1px solid var(--border); position: relative; z-index: 10; }
.header-inner { display: flex; align-items: center; justify-content: space-between; height: 64px; gap: 16px; }

.logo { display: inline-flex; align-items: center; gap: 10px; font-weight: 700; font-size: 1.15rem; letter-spacing: -.01em; text-decoration: none; color: var(--text); }
.logo:hover { color: var(--text); }
.logo img { display: block; }
.logo-accent { color: var(--accent); }

.header-nav { display: flex; align-items: center; gap: 4px; }
.header-link, .menu summary {
    color: var(--text); text-decoration: none; font-weight: 500; font-size: .95rem;
    padding: 8px 12px; border-radius: 8px; cursor: pointer;
}
.header-link:hover, .menu summary:hover, .menu[open] summary { background: var(--accent-soft); color: var(--accent); }

.menu { position: relative; }
.menu summary { list-style: none; display: flex; align-items: center; gap: 6px; }
.menu summary::-webkit-details-marker { display: none; }
.menu[open] summary svg { transform: rotate(180deg); }
.menu-panel {
    position: absolute; right: 0; top: calc(100% + 8px); width: min(480px, calc(100vw - 40px));
    display: grid; grid-template-columns: 1fr 1fr; gap: 4px; padding: 8px;
    background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: var(--shadow-lg);
}
.menu-panel a { display: block; padding: 10px 12px; border-radius: 10px; text-decoration: none; color: var(--text); }
.menu-panel a:hover, .menu-panel a.active { background: var(--accent-soft); }
.menu-panel strong { display: block; font-size: .95rem; font-weight: 600; }
.menu-panel span { display: block; font-size: .82rem; color: var(--muted); }

@media (max-width: 560px) {
    .header-link { display: none; }
    .menu-panel { grid-template-columns: 1fr; right: -8px; }
}

/* ---------- page head ---------- */

.page-head {
    padding: 40px 0 28px;
    background: radial-gradient(1200px 300px at 20% -40%, var(--accent-soft), transparent 70%);
}
h1 { font-size: clamp(1.7rem, 3.5vw, 2.3rem); line-height: 1.15; letter-spacing: -.025em; margin: 0 0 8px; font-weight: 700; }
.intro { color: var(--muted); font-size: 1.1rem; margin: 0; }

/* ---------- calculator ---------- */

.card { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); box-shadow: var(--shadow); }
.calc { padding: 24px; }

.calc form {
    display: grid; grid-template-columns: minmax(0, 330px) minmax(0, 1fr);
    column-gap: 32px; align-items: start;
}
/* Spacing via margins rather than row-gap, so the result spanning many implicit rows adds no height. */
.calc form > * { grid-column: 1; margin-top: 14px; }
.calc form > :first-child { margin-top: 0; }
.calc form > .result { grid-column: 2; grid-row: 1 / span 40; margin-top: 0; }
@media (max-width: 860px) {
    .calc { padding: 18px; }
    .calc form { grid-template-columns: minmax(0, 1fr); }
    .calc form > .result { grid-column: 1; grid-row: auto; margin-top: 18px; }
}

.calc form > .group-label { font-size: .75rem; font-weight: 600; letter-spacing: .06em; text-transform: uppercase; color: var(--muted); margin-bottom: -6px; }
.calc form > .group-label:not(:first-child) { margin-top: 20px; }
.grid { display: grid; gap: 10px; grid-template-columns: repeat(auto-fit, minmax(120px, 1fr)); }

label { display: grid; gap: 4px; font-size: .85rem; font-weight: 500; color: var(--muted); }
label.inline { display: flex; align-items: center; gap: 8px; font-weight: 400; color: var(--text); cursor: pointer; }
input[type=checkbox] { width: 16px; height: 16px; accent-color: var(--accent); }

input[type=text], textarea {
    font: 500 .95rem/1.4 var(--mono); color: var(--text); background: var(--bg);
    border: 1px solid var(--border-strong); border-radius: 10px; padding: 9px 12px; width: 100%;
    transition: border-color .15s, box-shadow .15s;
}
textarea { min-height: 150px; resize: vertical; font-size: .88rem; }
input[type=text]:focus, textarea:focus { outline: none; border-color: var(--accent); box-shadow: 0 0 0 3px var(--accent-soft); }

.actions { display: flex; gap: 8px; }
.btn, button {
    font: 600 .9rem/1 Inter, system-ui, sans-serif; cursor: pointer; border-radius: 10px; padding: 10px 16px;
    border: 1px solid var(--accent); background: var(--accent); color: #fff; text-decoration: none;
    display: inline-flex; align-items: center; gap: 6px; white-space: nowrap; transition: background .15s;
}
.btn:hover, button:hover { background: var(--accent-hover); color: #fff; }
.btn-secondary, button[type=reset], button.copy { background: transparent; color: var(--accent); border-color: var(--border-strong); }
.btn-secondary:hover, button[type=reset]:hover, button.copy:hover { background: var(--accent-soft); color: var(--accent); }
button.copy { padding: 6px 10px; font-size: .78rem; }

/* ---------- result ---------- */

.result { background: var(--panel); border: 1px solid var(--border); border-radius: 12px; padding: 20px; }
.result.error { background: var(--error-soft); border-color: transparent; color: var(--error); }
.result.error p { margin: 0; }

.answer { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.answer-label { color: var(--muted); font-size: .95rem; font-family: var(--mono); }
.answer-value { font: 600 2rem/1.1 var(--mono); letter-spacing: -.02em; word-break: break-all; }
.answer + .answer { margin-top: 12px; }
.note { color: var(--muted); font-size: .88rem; margin: 10px 0 0; }
.note.warn { color: var(--highlight); }

.chart { margin: 16px 0 4px; }
.chart svg { display: block; width: 100%; height: auto; }
.chart .gridline { stroke: var(--border); stroke-width: 1; }
.chart .axis { stroke: var(--border-strong); stroke-width: 1; }
.chart text { fill: var(--muted); font: 10px var(--mono); }
.chart .curve { fill: none; stroke: var(--accent); stroke-width: 2.25; stroke-linejoin: round; }
.chart .curve.extended { stroke-dasharray: 5 5; opacity: .6; }
.chart .pt { fill: var(--surface); stroke: var(--accent); stroke-width: 2.25; }
.chart .hl { fill: var(--highlight); stroke: var(--surface); stroke-width: 2; }
.chart .guide { stroke: var(--highlight); stroke-width: 1.25; stroke-dasharray: 3 4; }

.working { margin-top: 14px; border-top: 1px solid var(--border); padding-top: 12px; }
.working summary { cursor: pointer; font-weight: 600; font-size: .9rem; color: var(--text); }
.steps { list-style: none; counter-reset: step; padding: 0; margin: 10px 0 0; font-size: .88rem; overflow-wrap: anywhere; }
.steps li { counter-increment: step; position: relative; padding: 6px 0 6px 32px; border-bottom: 1px dashed var(--border); font-family: var(--mono); font-size: .82rem; }
.steps li:last-child { border-bottom: 0; }
.steps li::before {
    content: counter(step); position: absolute; left: 0; top: 6px; width: 20px; height: 20px; border-radius: 50%;
    background: var(--accent-soft); color: var(--accent); font: 600 .7rem/20px Inter, sans-serif; text-align: center;
}

.poly { font-family: var(--mono); font-size: .9rem; overflow-x: auto; margin: 12px 0 0; padding: 10px 12px; background: var(--surface); border: 1px solid var(--border); border-radius: 8px; }
.tag { font: 600 .7rem Inter, sans-serif; background: var(--accent-soft); color: var(--accent); padding: 2px 6px; border-radius: 4px; }

.table-wrap { overflow-x: auto; margin-bottom: 12px; }
table { border-collapse: collapse; width: 100%; font: .85rem var(--mono); }
th, td { text-align: left; padding: 8px 10px; border-bottom: 1px solid var(--border); }
th { font: 600 .72rem Inter, sans-serif; text-transform: uppercase; letter-spacing: .05em; color: var(--muted); }

.swatches { display: flex; gap: 12px; align-items: center; margin: 14px 0 0; }
.swatch { width: 52px; height: 52px; border-radius: 10px; border: 1px solid var(--border); flex: none; }
.ramp { display: flex; flex: 1; height: 28px; border-radius: 8px; overflow: hidden; border: 1px solid var(--border); }
.ramp span { flex: 1; }

/* ---------- content ---------- */

.page-grid { display: grid; grid-template-columns: minmax(0, 1fr) 260px; gap: 48px; margin-top: 40px; align-items: start; }
@media (max-width: 960px) { .page-grid { grid-template-columns: minmax(0, 1fr); gap: 24px; } }

.content { max-width: 720px; }
.content h2 { font-size: 1.3rem; letter-spacing: -.015em; margin: 36px 0 10px; }
.content h2:first-child { margin-top: 0; }
.content p, .content li { color: var(--text); }
.content ul, .content ol { padding-left: 1.3em; }

.formula {
    font: 500 1rem/1.7 var(--mono); background: var(--surface); border: 1px solid var(--border);
    border-left: 3px solid var(--accent); border-radius: 10px; padding: 14px 18px; overflow-x: auto; margin: 12px 0;
}

.more, .faq details { background: var(--surface); border: 1px solid var(--border); border-radius: 12px; margin: 8px 0; }
.more summary, .faq summary {
    cursor: pointer; font-weight: 600; padding: 14px 18px; list-style: none; display: flex; justify-content: space-between; gap: 12px;
}
.more summary::-webkit-details-marker, .faq summary::-webkit-details-marker { display: none; }
.more summary::after, .faq summary::after { content: "+"; color: var(--muted); font-weight: 400; font-size: 1.2rem; line-height: 1; }
.more[open] summary::after, .faq details[open] summary::after { content: "−"; }
.more > :not(summary), .faq details > p { padding: 0 18px; }
.more > :last-child, .faq details > p { margin-bottom: 16px; }
.faq details > p { margin-top: 0; color: var(--muted); }

.product {
    display: flex; align-items: center; gap: 16px; flex-wrap: wrap; margin: 36px 0 0; padding: 18px 20px;
    background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.product > div { flex: 1 1 240px; }
.product p { margin: 2px 0 0; color: var(--muted); font-size: .92rem; }

.sidebar { position: sticky; top: 20px; display: grid; gap: 20px; }
.side-nav { padding: 10px; }
.side-nav h2 { font-size: .72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); margin: 6px 10px 6px; }
.side-nav a { display: block; padding: 8px 10px; border-radius: 8px; text-decoration: none; color: var(--text); font-size: .92rem; }
.side-nav a:hover { background: var(--accent-soft); }
.side-nav a.active { background: var(--accent-soft); color: var(--accent); font-weight: 600; }

.ad { margin: 28px 0; min-height: 90px; }
.sidebar .ad { margin: 0; }

/* ---------- simple pages ---------- */

.page { padding-bottom: 20px; }
.page .card { padding: 24px; }

/* ---------- footer ---------- */

.site-footer { margin-top: 72px; border-top: 1px solid var(--border); background: var(--surface); font-size: .9rem; }
.footer-grid { display: grid; grid-template-columns: 1.3fr 1fr 1fr; gap: 32px; padding-top: 36px; padding-bottom: 24px; }
.footer-grid h2 { font-size: .72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--muted); margin: 4px 0 10px; }
.footer-grid ul { list-style: none; padding: 0; margin: 0; display: grid; gap: 6px; }
.footer-grid a:not(.logo) { color: var(--text); text-decoration: none; }
.footer-grid a:not(.logo):hover { color: var(--accent); }
.footer-bottom { border-top: 1px solid var(--border); padding-top: 16px; padding-bottom: 24px; font-size: .82rem; }
@media (max-width: 720px) { .footer-grid { grid-template-columns: 1fr; gap: 20px; } }