:root {
    color-scheme: light;

    /* Typography */
    --font-display: -apple-system, BlinkMacSystemFont, "SF Pro Display", "SF Pro Text",
        "Hiragino Kaku Gothic ProN", "Hiragino Sans", "Helvetica Neue", "Segoe UI", sans-serif;
    --font-body: -apple-system, BlinkMacSystemFont, "SF Pro Text",
        "Hiragino Kaku Gothic ProN", "Hiragino Sans", "Helvetica Neue", "Segoe UI", sans-serif;
    --text-hero: clamp(2.5rem, 5.5vw, 6rem);
    --text-h2: clamp(2rem, 3.2vw, 3rem);
    --text-h3: 1.5rem;
    --text-body: 1.0625rem;
    --text-caption: 0.875rem;
    --weight-heading: 600;
    --tracking-hero: -0.025em;
    --tracking-body: -0.01em;
    --leading-body: 1.7;

    /* Colors */
    --text: #1d1d1f;
    --text-secondary: #515154;
    --text-tertiary: #6e6e73;
    --bg-light: #ffffff;
    --bg-alt: #f5f5f7;
    --bg-dark: #000000;
    --text-on-dark: #f5f5f7;
    --link: #0066cc;
    --cta: #0071e3;
    --cta-hover: #0077ed;
    --cta-hover-aa: #0070df;
    --border-subtle: rgba(0, 0, 0, 0.12);
    --border-strong: rgba(0, 0, 0, 0.22);

    /* Layout */
    --content-max: 980px;
    --content-wide: 1200px;
    --section-py: clamp(80px, 12vw, 120px);
    --page-gutter: clamp(22px, 4vw, 48px);

    /* Radius and depth */
    --radius-pill: 980px;
    --radius-card: 18px;
    --shadow-card: 0 1px 3px rgba(0, 0, 0, 0.08);
    --shadow-card-hover: 0 8px 24px rgba(0, 0, 0, 0.09);

    /* Motion */
    --ease-apple: cubic-bezier(0.28, 0.11, 0.32, 1);
    --duration-fast: 150ms;
    --duration-base: 250ms;
    --duration-slow: 400ms;

    /* Compatibility aliases for existing static pages. */
    --bg: var(--bg-light);
    --bg-soft: var(--bg-alt);
    --fg: var(--text);
    --fg-soft: var(--text-secondary);
    --muted-fg: var(--text-tertiary);
    --border: var(--border-subtle);
    --primary: var(--cta);
    --primary-hover: var(--cta-hover-aa);
    --primary-fg: #ffffff;
    --radius: var(--radius-card);
    --radius-sm: 12px;
    --shadow-sm: var(--shadow-card);
    --shadow-md: var(--shadow-card-hover);
}

*,
*::before,
*::after {
    box-sizing: border-box;
}

html {
    scroll-behavior: smooth;
    scroll-padding-top: 48px;
    -webkit-text-size-adjust: 100%;
}

body {
    margin: 0;
    background: var(--bg-light);
    color: var(--text);
    font-family: var(--font-body);
    font-size: var(--text-body);
    line-height: var(--leading-body);
    letter-spacing: var(--tracking-body);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

button,
input,
select,
textarea {
    font: inherit;
}

a {
    color: var(--link);
}

:focus-visible {
    outline: 3px solid rgba(0, 102, 204, 0.55);
    outline-offset: 3px;
}

.nav {
    position: sticky;
    top: 0;
    z-index: 100;
    height: 48px;
    background: rgba(255, 255, 255, 0.72);
    border-bottom: 1px solid rgba(0, 0, 0, 0.08);
    backdrop-filter: saturate(180%) blur(20px);
    -webkit-backdrop-filter: saturate(180%) blur(20px);
}

.s-light,
.s-alt,
.s-dark {
    padding-block: var(--section-py);
}

.s-light {
    background: var(--bg-light);
    color: var(--text);
}

.s-alt {
    background: var(--bg-alt);
    color: var(--text);
}

.s-dark {
    background: var(--bg-dark);
    color: var(--text-on-dark);
}

.cta,
.btn-primary {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 6px;
    min-height: 44px;
    padding: 12px 22px;
    border: 1px solid var(--cta);
    border-radius: var(--radius-pill);
    background: var(--cta);
    color: #ffffff;
    font-weight: 600;
    font-size: 1rem;
    line-height: 1;
    letter-spacing: var(--tracking-body);
    text-decoration: none;
    transition: background-color var(--duration-fast) var(--ease-apple),
        border-color var(--duration-fast) var(--ease-apple),
        transform var(--duration-fast) var(--ease-apple);
}

.cta:hover,
.btn-primary:hover {
    border-color: var(--cta-hover-aa);
    background: var(--cta-hover-aa);
}

.cta:active,
.btn-primary:active {
    transform: scale(0.98);
}

.link-arrow {
    color: var(--link);
    font: 400 var(--text-body) / 1.47 var(--font-body);
    text-decoration: none;
}

.link-arrow::after {
    content: "\00a0\203a";
}

.link-arrow:hover {
    text-decoration: underline;
    text-underline-offset: 3px;
}

.apple-card {
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-card);
    background: var(--bg-light);
    box-shadow: var(--shadow-card);
}

.sr-only {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* Shared prompt and input document shell. */
:where(.document-page) {
    --theme-accent: var(--text-tertiary);
}

.document-page {
    min-height: 100dvh;
    background: var(--bg-alt);
    color: var(--text);
    line-height: 1.8;
}

.document-page .hero {
    position: relative;
    z-index: 1;
    padding: clamp(32px, 6vw, 52px) var(--page-gutter);
    border-bottom: 1px solid rgba(0, 0, 0, 0.08);
    background: var(--bg-light);
}

.document-page .hero-inner,
.document-page .container {
    width: 100%;
    max-width: 840px;
    margin-inline: auto;
}

.document-page .hero-inner::before {
    display: block;
    width: 36px;
    height: 3px;
    margin-bottom: 14px;
    border-radius: var(--radius-pill);
    background: var(--theme-accent);
    content: "";
}

.document-page .back {
    display: inline-flex;
    min-height: 36px;
    align-items: center;
    margin-bottom: 12px;
    color: var(--link);
    font-size: var(--text-caption);
    text-decoration: none;
}

.document-page .back:hover {
    text-decoration: underline;
    text-underline-offset: 3px;
}

.document-page .hero h1 {
    margin: 0;
    color: var(--text);
    font: 600 clamp(2rem, 4.5vw, 3rem) / 1.08 var(--font-display);
    letter-spacing: var(--tracking-hero);
    text-wrap: balance;
}

.document-page .hero .sub {
    max-width: 700px;
    margin: 12px 0 0;
    color: var(--text-secondary);
    font-size: var(--text-caption);
    line-height: 1.75;
}

.document-page .container {
    padding: clamp(36px, 6vw, 64px) var(--page-gutter) clamp(72px, 10vw, 112px);
}

.document-page .card {
    padding: clamp(24px, 5vw, 44px);
    border: 1px solid var(--border-subtle);
    border-radius: var(--radius-card);
    background: var(--bg-light);
    box-shadow: var(--shadow-card);
}

.document-page .card h2 {
    margin: 32px 0 12px;
    padding-left: 13px;
    border-left: 3px solid var(--border-strong);
    color: var(--text);
    font: 600 1.25rem / 1.4 var(--font-display);
    letter-spacing: -0.01em;
}

.document-page .card h2:first-of-type {
    margin-top: 0;
}

.document-page .card p {
    margin: 0 0 16px;
    color: var(--text-secondary);
}

.document-page .card ul,
.document-page .card ol {
    margin: 0 0 18px 1.5rem;
    color: var(--text-secondary);
}

.document-page .card li {
    margin-bottom: 6px;
}

.document-page .card strong {
    color: var(--text);
    font-weight: 600;
}

.document-page .card code,
.document-page .card pre,
.document-page .body-text {
    font-family: ui-monospace, "SFMono-Regular", Menlo, Monaco, Consolas, monospace;
}

.document-page .card code {
    padding: 2px 6px;
    border-radius: 6px;
    background: var(--bg-alt);
    color: var(--text);
    font-size: var(--text-caption);
}

.document-page .card pre {
    margin: 0 0 18px;
    padding: 18px;
    overflow-x: auto;
    border-radius: 12px;
    background: var(--text);
    color: var(--text-on-dark);
    font-size: var(--text-caption);
    line-height: 1.65;
}

.document-page .card pre code {
    padding: 0;
    background: transparent;
    color: inherit;
}

.document-page .card hr {
    margin: 28px 0;
    border: 0;
    border-top: 1px solid var(--border-subtle);
}

.document-page .meta {
    display: flex;
    flex-wrap: wrap;
    gap: 10px 20px;
    margin-top: 24px;
    padding-top: 18px;
    border-top: 1px solid var(--border-subtle);
    color: var(--text-tertiary);
    font-size: var(--text-caption);
}

.document-page .meta a {
    color: var(--link);
    text-decoration: none;
}

.document-page .meta a:hover {
    text-decoration: underline;
    text-underline-offset: 3px;
}

.document-page .stat-line {
    margin-bottom: 20px;
    padding-bottom: 16px;
    border-bottom: 1px solid var(--border-subtle);
    color: var(--text-secondary);
    font-size: var(--text-caption);
    line-height: 1.7;
}

.document-page .body-text {
    margin: 0;
    white-space: pre-wrap;
    color: var(--text);
    font-family: var(--font-body);
    font-size: 1rem;
    line-height: 1.95;
}

@media (max-width: 600px) {
    .document-page .hero {
        padding-block: 28px;
    }

    .document-page .card {
        padding: 24px 20px;
        border-radius: 16px;
    }
}

@supports (word-break: auto-phrase) {
    @media (min-width: 735px) {
        h1,
        h2,
        h3 {
            word-break: auto-phrase;
        }
    }
}

@media (prefers-reduced-motion: reduce) {
    html {
        scroll-behavior: auto;
    }

    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
        scroll-behavior: auto !important;
    }
}