:root {
    --bg: var(--obs-bg, #080d15);
    --panel: var(--obs-panel, #111923);
    --panel-strong: var(--obs-panel-raised, #182331);
    --text: var(--obs-text, #f1f5f8);
    --muted: var(--obs-muted, #b5bec9);
    --soft: var(--obs-text, #f1f5f8);
    --line: var(--obs-line, rgba(218, 229, 239, 0.16));
    --cyan: var(--obs-interaction, #62d7df);
    --violet: var(--obs-data-violet, #ab95c5);
    --pink: var(--obs-data-vermilion, #d87d61);
    --shadow: var(--obs-shadow, 0 12px 32px rgba(0, 0, 0, 0.2));
}

* {
    box-sizing: border-box;
}

body {
    margin: 0;
    min-height: 100vh;
    background: var(--bg);
    color: var(--text);
    font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

a {
    color: inherit;
}

.sp-header {
    position: sticky;
    top: 0;
    z-index: 20;
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 20px;
    min-height: 64px;
    padding: 0 28px;
    border-bottom: 1px solid var(--line);
    background: rgba(8, 9, 20, 0.86);
    backdrop-filter: blur(16px);
}

.sp-logo {
    color: var(--cyan);
    font-weight: 700;
    text-decoration: none;
    white-space: nowrap;
}

.sp-nav {
    display: flex;
    align-items: center;
    gap: 6px;
}

.sp-nav a,
.sp-menu summary {
    display: inline-flex;
    min-height: 36px;
    align-items: center;
    border-radius: 8px;
    padding: 0 12px;
    color: var(--muted);
    font-size: 0.92rem;
    text-decoration: none;
}

.sp-nav a:hover,
.sp-menu summary:hover {
    background: rgba(255, 255, 255, 0.07);
    color: var(--text);
}

.sp-menu {
    position: relative;
}

.sp-menu summary {
    cursor: pointer;
    list-style: none;
}

.sp-menu summary::-webkit-details-marker {
    display: none;
}

.sp-menu-panel {
    position: absolute;
    right: 0;
    top: calc(100% + 8px);
    display: grid;
    width: 230px;
    padding: 8px;
    border: 1px solid var(--line);
    border-radius: 10px;
    background: #111327;
    box-shadow: 0 18px 50px rgba(0, 0, 0, 0.34);
}

.sp-main {
    width: min(1160px, calc(100% - 32px));
    margin: 0 auto;
}

.sp-hero {
    min-height: calc(100vh - 64px);
    display: grid;
    align-content: center;
    gap: 24px;
    padding: 64px 0;
    text-align: center;
}

.sp-kicker {
    color: var(--cyan);
    font-size: 0.78rem;
    font-weight: 700;
    letter-spacing: 0.12em;
    text-transform: uppercase;
}

.sp-hero h1,
.sp-page-head h1 {
    max-width: 900px;
    margin: 0 auto;
    font-size: clamp(2.4rem, 8vw, 5.8rem);
    line-height: 1;
}

.sp-hero p,
.sp-page-head p {
    max-width: 760px;
    margin: 0 auto;
    color: var(--muted);
    font-size: 1.08rem;
    line-height: 1.7;
}

.sp-actions {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 12px;
}

.sp-button,
.icon-button {
    display: inline-flex;
    min-height: 42px;
    align-items: center;
    justify-content: center;
    border: 1px solid var(--line);
    border-radius: 8px;
    background: rgba(255, 255, 255, 0.05);
    color: var(--text);
    padding: 0 16px;
    font: inherit;
    text-decoration: none;
    cursor: pointer;
}

.sp-button.primary {
    border-color: rgba(0, 221, 255, 0.32);
    background: rgba(0, 221, 255, 0.14);
    color: var(--cyan);
}

.sp-grid-section,
.theory-layout,
.paper-list,
.sp-split,
.sp-band {
    margin: 34px 0 72px;
}

.sp-section-heading {
    margin-bottom: 22px;
}

.sp-section-heading span {
    color: var(--cyan);
    font-size: 0.76rem;
    font-weight: 700;
    letter-spacing: 0.12em;
    text-transform: uppercase;
}

.sp-section-heading h2,
.sp-split h2,
.sp-band h2 {
    margin: 8px 0 0;
    font-size: clamp(1.6rem, 4vw, 2.4rem);
}

.explorer-grid,
.theory-layout {
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 16px;
}

.explorer-card,
.theory-panel,
.paper-card,
.sp-callout,
.sp-band {
    border: 1px solid var(--line);
    border-radius: 8px;
    background: var(--panel);
}

.explorer-card {
    min-height: 230px;
    display: grid;
    align-content: end;
    padding: 20px;
    text-decoration: none;
    transition: transform 180ms ease, border-color 180ms ease;
}

.explorer-card:hover {
    border-color: color-mix(in srgb, var(--accent) 55%, white 10%);
    transform: translateY(-3px);
}

.card-symbol {
    color: var(--accent);
    font-size: 2.5rem;
    font-weight: 800;
}

.explorer-card h3,
.theory-panel h2,
.paper-card h2 {
    margin: 14px 0 8px;
}

.explorer-card p,
.theory-panel p,
.paper-card p,
.sp-split p,
.sp-band p {
    color: var(--muted);
    line-height: 1.65;
}

.explorer-card span,
.invariant-pill {
    width: fit-content;
    border-radius: 999px;
    background: rgba(255, 255, 255, 0.07);
    color: var(--muted);
    padding: 6px 10px;
    font-size: 0.8rem;
}

.sp-page-head {
    display: grid;
    gap: 18px;
    padding: 84px 0 34px;
    text-align: center;
}

.theory-panel,
.paper-card,
.sp-callout,
.sp-band {
    padding: 22px;
}

.sp-split {
    display: grid;
    grid-template-columns: 1.4fr 1fr;
    gap: 16px;
    align-items: start;
}

.paper-list {
    display: grid;
    gap: 16px;
}

.paper-card {
    display: flex;
    align-items: center;
    justify-content: space-between;
    gap: 18px;
}

.paper-missing {
    color: #fca5a5;
}

.explorer-shell {
    display: grid;
    grid-template-columns: minmax(280px, 380px) 1fr;
    gap: 18px;
    min-height: calc(100vh - 120px);
    padding: 28px 0;
}

.explorer-info,
.viewer-panel {
    border: 1px solid var(--line);
    border-radius: 8px;
    background: rgba(17, 19, 39, 0.76);
}

.explorer-info {
    display: grid;
    align-content: start;
    gap: 16px;
    padding: 22px;
}

.explorer-info h1 {
    margin: 0;
    font-size: clamp(2rem, 4vw, 3.4rem);
}

.explorer-info p {
    color: var(--muted);
    line-height: 1.65;
}

.back-link {
    color: var(--muted);
    font-size: 0.9rem;
    text-decoration: none;
}

.control-panel {
    display: grid;
    gap: 12px;
    margin-top: 8px;
}

.range-control,
.check-control {
    display: grid;
    gap: 8px;
    color: var(--muted);
    font-size: 0.9rem;
}

.range-control input {
    width: 100%;
    accent-color: var(--accent);
}

.check-control {
    grid-template-columns: auto 1fr;
    align-items: center;
}

.viewer-panel {
    position: relative;
    overflow: hidden;
    border: 0;
    border-radius: 0;
    background: transparent;
    min-height: 620px;
}

.topology-viewer {
    width: 100%;
    height: 100%;
    min-height: 620px;
}

.viewer-status {
    position: absolute;
    left: 14px;
    bottom: 14px;
    max-width: calc(100% - 28px);
    border: 1px solid var(--line);
    border-radius: 8px;
    background: rgba(8, 9, 20, 0.72);
    color: var(--muted);
    padding: 8px 10px;
    font-size: 0.86rem;
}

.sp-footer {
    display: flex;
    justify-content: center;
    gap: 14px;
    padding: 30px 16px;
    border-top: 1px solid var(--line);
    color: var(--muted);
    font-size: 0.9rem;
}

@media (max-width: 860px) {
    .sp-header,
    .sp-nav,
    .sp-footer {
        flex-wrap: wrap;
        justify-content: center;
    }

    .explorer-grid,
    .theory-layout,
    .sp-split,
    .explorer-shell {
        grid-template-columns: 1fr;
    }

    .paper-card {
        align-items: start;
        flex-direction: column;
    }

    .viewer-panel {
        order: -1;
    }

    .viewer-panel,
    .topology-viewer {
        min-height: 62vh;
    }
}

/* Learning-first homepage and guided explorer refinements. */
html { scroll-behavior: smooth; }
body {
    min-width: 320px;
    background: var(--bg);
    font-size: 16px;
}

:focus-visible { outline: 3px solid var(--cyan); outline-offset: 3px; }
.sp-header { min-height: 68px; background: rgba(7, 10, 19, 0.88); backdrop-filter: blur(18px); }
.sp-logo { color: var(--text); font-weight: 750; letter-spacing: -0.02em; }
.sp-logo::before {
    display: inline-block;
    width: 0.55em;
    height: 0.55em;
    margin-right: 0.55em;
    border: 1px solid var(--cyan);
    border-radius: 50%;
    content: "";
}

.sp-main { width: min(1180px, calc(100% - 40px)); }
.sp-kicker,
.eyebrow { font-size: 0.8125rem; line-height: 1.35; }
.sp-home-hero {
    grid-template-columns: minmax(0, 1.1fr) minmax(290px, 0.7fr);
    align-items: center;
    min-height: 500px;
    gap: clamp(28px, 6vw, 72px);
    padding: clamp(56px, 9vw, 110px) 0 clamp(48px, 7vw, 84px);
    text-align: left;
}

.sp-hero-copy { display: grid; gap: 24px; align-items: start; }
.sp-hero h1,
.sp-page-head h1 {
    max-width: 760px;
    margin: 0;
    font-size: clamp(2.8rem, 6.5vw, 5.3rem);
    letter-spacing: -0.065em;
    line-height: 0.98;
}

.sp-hero p,
.sp-page-head p { margin: 0; font-size: clamp(1rem, 1.7vw, 1.125rem); }
.sp-actions { justify-content: start; }
.sp-button,
.icon-button {
    gap: 9px;
    min-height: 44px;
    border-radius: 8px;
    font-weight: 650;
    transition: border-color 160ms ease, background 160ms ease, transform 160ms ease;
}

.sp-button:hover,
.icon-button:hover { border-color: rgba(244, 247, 251, 0.44); background: rgba(255, 255, 255, 0.085); transform: translateY(-1px); }
.sp-button.primary,
.primary-control { border-color: color-mix(in srgb, var(--cyan) 50%, transparent); background: color-mix(in srgb, var(--cyan) 14%, transparent); color: #e9fcff; }
.sp-button.primary:hover,
.primary-control:hover { border-color: var(--cyan); background: color-mix(in srgb, var(--cyan) 20%, transparent); }

.learning-card,
.explorer-card,
.theory-panel,
.paper-card,
.sp-callout,
.sp-band,
.explorer-info,
.viewer-panel,
.explorer-reflection {
    border: 1px solid var(--line);
    background: var(--panel);
    box-shadow: var(--shadow);
}

.learning-card { padding: clamp(24px, 4vw, 36px); border-radius: 16px; }
.learning-steps { display: grid; gap: 22px; padding: 0; margin: 26px 0 0; list-style: none; }
.learning-steps li { display: grid; grid-template-columns: 35px 1fr; gap: 13px; }
.learning-steps li > span { color: var(--cyan); font-size: 0.8rem; font-weight: 750; letter-spacing: 0.08em; }
.learning-steps strong { display: block; margin-bottom: 3px; color: var(--soft); }
.learning-steps p { margin: 0; color: var(--muted); font-size: 0.94rem; line-height: 1.5; }

.sp-grid-section,
.theory-layout,
.paper-list,
.sp-split,
.sp-band { margin-bottom: 88px; }

.sp-section-heading { max-width: 690px; margin-bottom: 24px; }
.sp-section-heading h2,
.sp-split h2,
.sp-band h2,
.explorer-reflection h2 { margin: 8px 0 10px; font-size: clamp(1.8rem, 4vw, 2.65rem); letter-spacing: -0.045em; line-height: 1.08; }
.sp-section-heading p { margin: 0; color: var(--muted); line-height: 1.65; }

.explorer-card { display: grid; align-content: start; min-height: 270px; padding: 20px; border-radius: 12px; }
.explorer-card:hover { border-color: color-mix(in srgb, var(--accent) 68%, white 12%); background: color-mix(in srgb, var(--accent) 9%, var(--panel)); }
.card-topline { display: flex; align-items: center; justify-content: space-between; gap: 12px; }
.card-symbol { font-size: 2.15rem; line-height: 1; }
.card-level { color: var(--muted); font-size: 0.8125rem; text-align: right; }
.explorer-card h3 { margin: 28px 0 8px; font-size: 1.25rem; letter-spacing: -0.025em; }
.explorer-card > span:not(.card-link),
.invariant-pill { margin-top: 15px; color: var(--soft); font-size: 0.78rem; }
.card-link { align-self: end; margin-top: 24px; color: var(--accent); font-size: 0.9rem; font-weight: 700; }
.card-link b { margin-left: 3px; font-size: 1rem; }

.theory-panel,
.paper-card,
.sp-callout,
.sp-band { border-radius: 12px; }
.text-link { display: inline-block; margin-top: 16px; color: var(--cyan); font-weight: 700; }
.sp-page-head { text-align: left; }

.explorer-shell { grid-template-columns: minmax(285px, 0.72fr) minmax(0, 1.28fr); gap: 18px; padding: 28px 0 18px; }
.explorer-info { gap: 17px; padding: clamp(20px, 3vw, 30px); border-radius: 14px; }
.explorer-info h1 { font-size: clamp(2rem, 4vw, 3.2rem); letter-spacing: -0.055em; line-height: 0.98; }
.explorer-info > p { margin: 0; }
.model-scope { padding: 10px 12px; border-left: 2px solid var(--violet); background: rgba(255, 255, 255, 0.035); color: var(--muted); font-size: .87rem; line-height: 1.5; }
.model-scope strong { color: var(--soft); }
.back-link { width: fit-content; }
.invariant-pill { margin-top: 0; }

.observation-card { padding: 16px; border-left: 2px solid var(--accent); background: rgba(3, 8, 19, 0.34); }
.observation-card h2 { margin: 7px 0 0; color: var(--soft); font-size: 1rem; font-weight: 620; line-height: 1.5; }
.control-panel { gap: 16px; padding-top: 2px; }
.controls-heading p { margin: 6px 0 0; color: var(--muted); font-size: 0.9rem; line-height: 1.48; }
.control-actions { display: flex; flex-wrap: wrap; gap: 8px; }
.icon-button { min-height: 40px; font-size: 0.9rem; }
.range-control,
.check-control { gap: 7px; color: var(--soft); font-size: 0.9rem; }
.range-control > span { display: flex; align-items: center; justify-content: space-between; gap: 12px; font-weight: 700; }
.range-control output { min-width: 3.2ch; color: var(--cyan); font-family: ui-monospace, SFMono-Regular, Menlo, monospace; font-size: 0.85rem; font-weight: 650; text-align: right; }
.range-control small,
.check-control small { color: var(--muted); font-size: 0.8rem; font-weight: 400; line-height: 1.4; }
.check-control { align-items: start; padding: 3px 0; }
.check-control input { width: 17px; height: 17px; margin: 2px 0 0; accent-color: var(--accent); }
.check-control span { display: grid; gap: 2px; }

.viewer-panel { display: grid; grid-template-rows: auto 1fr; min-height: 660px; overflow: hidden; border: 1px solid var(--line); border-radius: 14px; background: #09101e; }
.viewer-header { z-index: 1; display: flex; align-items: center; justify-content: space-between; gap: 16px; padding: 18px 20px 15px; border-bottom: 1px solid var(--line); background: rgba(9, 14, 27, 0.84); }
.viewer-header strong { display: block; margin-top: 3px; color: var(--soft); font-size: 1rem; }
.viewer-gestures { display: flex; flex-wrap: wrap; justify-content: end; gap: 7px; color: var(--muted); font-size: 0.78rem; }
.viewer-gestures span,
.viewer-legend span { padding: 4px 7px; border-radius: 999px; background: rgba(255, 255, 255, 0.06); }
.topology-viewer { min-height: 570px; }
.topology-viewer canvas { display: block; width: 100%; height: 100%; }
.viewer-status { bottom: 16px; color: var(--soft); }
.viewer-legend { position: absolute; right: 14px; bottom: 16px; display: flex; flex-wrap: wrap; justify-content: end; gap: 7px; color: var(--muted); font-size: 0.76rem; }
.legend-dot { display: inline-block; width: 7px; height: 7px; margin-right: 4px; border-radius: 50%; background: #fff; vertical-align: 1px; }
.legend-grid { display: inline-block; width: 8px; height: 8px; margin-right: 4px; border: 1px solid var(--accent); vertical-align: -1px; }

.explorer-reflection { display: flex; align-items: center; justify-content: space-between; gap: 24px; margin: 0 0 88px; padding: clamp(24px, 4vw, 36px); border-radius: 14px; border-left: 3px solid var(--accent); }
.explorer-reflection > div { max-width: 690px; }

@media (max-width: 920px) {
    .sp-header { flex-wrap: wrap; justify-content: center; padding: 10px 20px; }
    .sp-nav { flex-wrap: wrap; justify-content: center; }
    .sp-home-hero,
    .explorer-shell,
    .sp-split { grid-template-columns: 1fr; }
    .explorer-grid,
    .theory-layout { grid-template-columns: repeat(2, minmax(0, 1fr)); }
    .viewer-panel { order: initial; }
    .viewer-panel { min-height: min(720px, 82vh); }
    .topology-viewer { min-height: min(620px, 72vh); }
}

@media (max-width: 620px) {
    .sp-main { width: min(100% - 28px, 1180px); }
    .sp-header { gap: 3px; }
    .sp-nav { gap: 0; }
    .sp-nav a,
    .sp-menu summary { min-height: 34px; padding: 0 8px; font-size: 0.81rem; }
    .sp-home-hero { min-height: 0; padding: 54px 0; }
    .sp-hero h1,
    .sp-page-head h1 { font-size: clamp(2.55rem, 13vw, 3.5rem); }
    .explorer-grid,
    .theory-layout { grid-template-columns: 1fr; }
    .explorer-card { min-height: 238px; }
    .paper-card,
    .explorer-reflection { align-items: start; flex-direction: column; }
    .viewer-panel { min-height: 560px; }
    .topology-viewer { min-height: 480px; }
    .viewer-header { align-items: start; flex-direction: column; }
    .viewer-gestures { justify-content: start; }
    .viewer-status { right: 14px; bottom: 50px; }
    .viewer-legend { right: auto; left: 14px; bottom: 14px; justify-content: start; }
}

@media (prefers-reduced-motion: reduce) {
    html { scroll-behavior: auto; }
    *, *::before, *::after { transition-duration: 0.01ms !important; animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; }
}