/* ============================================================
   3RK — Common Design System
   Style philosophy: Vercel precision × Anthropic restraint ×
   Linear density × Apple rhythm × Stripe hierarchy
   Monochrome-first. Product UI, not blog.
   ============================================================ */


/* ============================================================
   1. DESIGN TOKENS
   ============================================================ */

:root {

  /* Color — monochrome base */
  --color-black:        #0a0a0a;
  --color-ink:          #111111;
  --color-ink-soft:     #333333;
  --color-mid:          #666666;
  --color-muted:        #999999;
  --color-line:         #e5e5e5;
  --color-surface:      #f7f7f7;
  --color-white:        #ffffff;

  /* Accent — single controlled touch of color */
  --color-accent:       #0070f3;   /* swap for brand color when ready */
  --color-accent-hover: #005fd4;

  /* Typography */
  --font-sans: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI',
               Helvetica, Arial, sans-serif;
  --font-mono: 'JetBrains Mono', 'Fira Code', 'SF Mono', monospace;

  /* Type scale — fluid, restrained */
  --text-xs:   0.75rem;   /* 12px */
  --text-sm:   0.875rem;  /* 14px */
  --text-base: 1rem;      /* 16px */
  --text-md:   1.125rem;  /* 18px */
  --text-lg:   1.25rem;   /* 20px */
  --text-xl:   1.5rem;    /* 24px */
  --text-2xl:  2rem;      /* 32px */
  --text-3xl:  2.5rem;    /* 40px */
  --text-4xl:  3.25rem;   /* 52px */
  --text-5xl:  4rem;      /* 64px */

  /* Weight */
  --weight-normal:   400;
  --weight-medium:   500;
  --weight-semibold: 600;
  --weight-bold:     700;

  /* Leading */
  --leading-tight:  1.15;
  --leading-snug:   1.3;
  --leading-normal: 1.5;
  --leading-loose:  1.75;

  /* Letter spacing */
  --tracking-tight:  -0.03em;
  --tracking-snug:   -0.02em;
  --tracking-normal:  0em;
  --tracking-wide:    0.06em;
  --tracking-widest:  0.12em;

  /* Spacing — 4px base unit */
  --space-1:  0.25rem;   /* 4px  */
  --space-2:  0.5rem;    /* 8px  */
  --space-3:  0.75rem;   /* 12px */
  --space-4:  1rem;      /* 16px */
  --space-5:  1.25rem;   /* 20px */
  --space-6:  1.5rem;    /* 24px */
  --space-8:  2rem;      /* 32px */
  --space-10: 2.5rem;    /* 40px */
  --space-12: 3rem;      /* 48px */
  --space-16: 4rem;      /* 64px */
  --space-20: 5rem;      /* 80px */
  --space-24: 6rem;      /* 96px */
  --space-32: 8rem;      /* 128px */

  /* Layout */
  --container-xs:  480px;
  --container-sm:  640px;
  --container-md:  768px;
  --container-lg:  1024px;
  --container-xl:  1200px;
  --container-max: 1440px;

  /* Border */
  --radius-sm: 4px;
  --radius-md: 8px;
  --radius-lg: 12px;

  /* Transition */
  --ease-out:  cubic-bezier(0.16, 1, 0.3, 1);
  --ease-in:   cubic-bezier(0.4, 0, 1, 1);
  --duration:  180ms;
  --duration-slow: 300ms;

  /* Header */
  --header-height: 56px;
}


/* ============================================================
   2. RESET
   Lightweight — preserves useful browser defaults
   ============================================================ */

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  font-size: 16px;
  -webkit-text-size-adjust: 100%;
  text-size-adjust: 100%;
  scroll-behavior: smooth;
  hanging-punctuation: first last;
}

body {
  font-family: var(--font-sans);
  font-size: var(--text-base);
  font-weight: var(--weight-normal);
  line-height: var(--leading-loose);
  color: var(--color-ink);
  background: var(--color-white);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-feature-settings: 'kern' 1, 'liga' 1, 'calt' 1;
}

img, video, svg {
  display: block;
  max-width: 100%;
  height: auto;
}

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

p, h1, h2, h3, h4, h5, h6 {
  overflow-wrap: break-word;
}

a {
  color: inherit;
  text-decoration: none;
}

ul, ol {
  list-style: none;
}

button {
  background: none;
  border: none;
  cursor: pointer;
}


/* ============================================================
   3. TYPOGRAPHY
   Rhythm: tight headings, spacious body
   ============================================================ */

h1, h2, h3, h4 {
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-snug);
  color: var(--color-ink);
  text-wrap: balance;
}

h1 {
  font-size: clamp(var(--text-3xl), 5vw, var(--text-5xl));
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-tight);
  font-weight: var(--weight-bold);
}

h2 {
  font-size: clamp(var(--text-2xl), 3.5vw, var(--text-4xl));
  line-height: var(--leading-tight);
  letter-spacing: var(--tracking-snug);
}

h3 {
  font-size: clamp(var(--text-xl), 2.5vw, var(--text-2xl));
  line-height: var(--leading-snug);
}

h4 {
  font-size: var(--text-lg);
  line-height: var(--leading-snug);
}

p {
  font-size: var(--text-base);
  line-height: var(--leading-loose);
  color: var(--color-ink-soft);
  max-width: 68ch;
}

/* Meta / label text */
.meta {
  font-size: var(--text-sm);
  line-height: var(--leading-normal);
  color: var(--color-muted);
  letter-spacing: var(--tracking-wide);
}

/* Eyebrow label */
.label {
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-widest);
  text-transform: uppercase;
  color: var(--color-muted);
}

/* Large body — introductory paragraphs */
.lead {
  font-size: var(--text-lg);
  line-height: var(--leading-loose);
  color: var(--color-ink-soft);
  max-width: 60ch;
}

/* Mono — for dates, codes, tags */
.mono {
  font-family: var(--font-mono);
  font-size: var(--text-sm);
  color: var(--color-muted);
}


/* ============================================================
   4. LAYOUT
   ============================================================ */

/* Centered container with consistent lateral breathing room */
.container {
  width: 100%;
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--space-8);
}

.container--narrow {
  max-width: var(--container-md);
}

.container--wide {
  max-width: var(--container-max);
}

/* Section vertical rhythm */
.section {
  padding-block: var(--space-24);
}

.section--sm {
  padding-block: var(--space-16);
}

.section--lg {
  padding-block: var(--space-32);
}

/* Divider — hairline, no shadow */
.divider {
  border: none;
  border-top: 1px solid var(--color-line);
  margin-block: 0;
}

/* Two-column grid — content + sidebar-less wide layouts */
.grid-2 {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: var(--space-8);
}

.grid-3 {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-8);
}

/* Stack utility */
.stack {
  display: flex;
  flex-direction: column;
}

.stack--sm  { gap: var(--space-4); }
.stack--md  { gap: var(--space-8); }
.stack--lg  { gap: var(--space-16); }

/* Cluster — horizontal flex */
.cluster {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: var(--space-4);
}


/* ============================================================
   5. HEADER / NAVIGATION
   Fixed, minimal — content surfaces behind it
   ============================================================ */

.site-header {
  position: fixed;
  inset-block-start: 0;
  inset-inline: 0;
  height: var(--header-height);
  z-index: 100;
  background: rgba(255, 255, 255, 0.88);
  backdrop-filter: saturate(180%) blur(16px);
  -webkit-backdrop-filter: saturate(180%) blur(16px);
  border-bottom: 1px solid var(--color-line);
}

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--space-8);
}

/* Logo */
.site-logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-base);
  font-weight: var(--weight-bold);
  letter-spacing: var(--tracking-tight);
  color: var(--color-ink);
  user-select: none;
}

.site-logo img {
  height: 24px;
  width: auto;
}

/* Nav — right side */
.site-nav {
  display: flex;
  align-items: center;
  gap: var(--space-8);
}

.site-nav__link {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-mid);
  transition: color var(--duration) var(--ease-out);
}

.site-nav__link:hover,
.site-nav__link[aria-current="page"] {
  color: var(--color-ink);
}

/* CTA in header */
.site-nav__cta {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-white);
  background: var(--color-ink);
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-sm);
  transition: background var(--duration) var(--ease-out),
              opacity var(--duration) var(--ease-out);
}

.site-nav__cta:hover {
  background: var(--color-ink-soft);
}

/* Offset page content below fixed header */
.page-body {
  padding-block-start: var(--header-height);
}


/* ============================================================
   6. HERO
   Statement-first — like Anthropic / Stripe landings
   ============================================================ */

.hero {
  padding-block: var(--space-32) var(--space-24);
  border-bottom: 1px solid var(--color-line);
}

.hero__label {
  margin-bottom: var(--space-6);
}

.hero__headline {
  margin-bottom: var(--space-6);
  max-width: 20ch;
}

.hero__sub {
  margin-bottom: var(--space-10);
}

.hero__actions {
  display: flex;
  gap: var(--space-4);
  align-items: center;
}


/* ============================================================
   7. FEATURED BLOCK
   Single article, high visual weight — editorial decision
   ============================================================ */

.featured {
  padding-block: var(--space-16);
  border-bottom: 1px solid var(--color-line);
}

.featured__label {
  margin-bottom: var(--space-6);
}

.featured__inner {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-16);
  align-items: start;
}

.featured__content {}

.featured__category {
  margin-bottom: var(--space-4);
}

.featured__title {
  margin-bottom: var(--space-5);
  font-size: clamp(var(--text-xl), 3vw, var(--text-3xl));
  line-height: var(--leading-snug);
  letter-spacing: var(--tracking-tight);
}

.featured__title a {
  transition: opacity var(--duration) var(--ease-out);
}

.featured__title a:hover {
  opacity: 0.6;
}

.featured__excerpt {
  margin-bottom: var(--space-6);
}

.featured__meta {
  display: flex;
  gap: var(--space-4);
  align-items: center;
}

/* Featured image placeholder — aspect-ratio locked */
.featured__image {
  aspect-ratio: 16 / 10;
  background: var(--color-surface);
  border-radius: var(--radius-md);
  overflow: hidden;
}

.featured__image img {
  width: 100%;
  height: 100%;
  object-fit: cover;
}


/* ============================================================
   8. ARTICLE LIST
   Linear-style — dense, scannable, date-anchored
   ============================================================ */

.article-list {}

/* Individual row — Linear changelog row */
.article-row {
  display: grid;
  grid-template-columns: 160px 1fr;
  gap: var(--space-8);
  padding-block: var(--space-6);
  border-bottom: 1px solid var(--color-line);
  align-items: start;
  transition: background var(--duration) var(--ease-out);
}

.article-row:first-child {
  border-top: 1px solid var(--color-line);
}

.article-row:hover {
  background: var(--color-surface);
  margin-inline: calc(-1 * var(--space-4));
  padding-inline: var(--space-4);
  border-radius: var(--radius-sm);
}

.article-row__date {
  padding-block-start: var(--space-1);
  white-space: nowrap;
}

.article-row__body {}

.article-row__category {
  margin-bottom: var(--space-2);
}

.article-row__title {
  font-size: var(--text-md);
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-snug);
  line-height: var(--leading-snug);
  margin-bottom: var(--space-2);
}

.article-row__title a {
  transition: opacity var(--duration) var(--ease-out);
}

.article-row__title a:hover {
  opacity: 0.55;
}

.article-row__summary {
  font-size: var(--text-sm);
  line-height: var(--leading-normal);
  color: var(--color-mid);
  max-width: 72ch;
}


/* ============================================================
   9. CARD GRID
   For topic pages and secondary lists
   ============================================================ */

.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: var(--space-1);  /* tight gap — product grid feel */
}

.card {
  padding: var(--space-8);
  background: var(--color-white);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
  transition: border-color var(--duration) var(--ease-out),
              background var(--duration) var(--ease-out);
}

.card:hover {
  border-color: var(--color-mid);
  background: var(--color-surface);
}

.card__icon {
  font-size: var(--text-xl);
  line-height: 1;
  margin-bottom: var(--space-2);
}

.card__title {
  font-size: var(--text-base);
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-snug);
  color: var(--color-ink);
}

.card__desc {
  font-size: var(--text-sm);
  color: var(--color-mid);
  line-height: var(--leading-normal);
  max-width: none;
}

.card__link {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-ink);
  margin-block-start: auto;
  display: flex;
  align-items: center;
  gap: var(--space-1);
  transition: opacity var(--duration) var(--ease-out);
}

.card__link:hover {
  opacity: 0.55;
}

.card__link::after {
  content: '→';
}


/* ============================================================
   10. TOPIC SECTION
   Notion-style categorized blocks — structured, not random
   ============================================================ */

.topic-section {
  padding-block: var(--space-16);
  border-bottom: 1px solid var(--color-line);
}

.topic-section__header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: var(--space-8);
}

.topic-section__title {
  font-size: var(--text-lg);
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-snug);
}

.topic-section__all {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-muted);
  transition: color var(--duration) var(--ease-out);
}

.topic-section__all:hover {
  color: var(--color-ink);
}


/* ============================================================
   11. MANIFESTO LAYOUT
   About / long-form structured text — Apple Newsroom rhythm
   ============================================================ */

.manifesto {
  max-width: var(--container-md);
  margin-inline: auto;
}

.manifesto__section {
  padding-block: var(--space-20);
  border-bottom: 1px solid var(--color-line);
}

.manifesto__section:last-child {
  border-bottom: none;
}

.manifesto__heading {
  font-size: clamp(var(--text-xl), 3vw, var(--text-3xl));
  letter-spacing: var(--tracking-tight);
  line-height: var(--leading-snug);
  margin-bottom: var(--space-8);
  max-width: 28ch;
}

.manifesto__body p {
  font-size: var(--text-md);
  line-height: var(--leading-loose);
  color: var(--color-ink-soft);
  margin-bottom: var(--space-6);
  max-width: 64ch;
}

.manifesto__body p:last-child {
  margin-bottom: 0;
}

.manifesto__body strong {
  font-weight: var(--weight-semibold);
  color: var(--color-ink);
}

.manifesto__body em {
  font-style: italic;
}

/* Three keys — structured trio */
.keys-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-8);
  margin-block-start: var(--space-10);
}

.key-block {
  padding-block-start: var(--space-6);
  border-top: 2px solid var(--color-ink);
}

.key-block__title {
  font-size: var(--text-base);
  font-weight: var(--weight-bold);
  letter-spacing: var(--tracking-wide);
  text-transform: uppercase;
  margin-bottom: var(--space-4);
}

.key-block__desc {
  font-size: var(--text-sm);
  line-height: var(--leading-loose);
  color: var(--color-mid);
  max-width: none;
}


/* ============================================================
   12. UI ELEMENTS
   ============================================================ */

/* --- Buttons --- */

.btn {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  line-height: 1;
  padding: var(--space-3) var(--space-5);
  border-radius: var(--radius-sm);
  border: 1px solid transparent;
  cursor: pointer;
  transition: background var(--duration) var(--ease-out),
              border-color var(--duration) var(--ease-out),
              color var(--duration) var(--ease-out),
              opacity var(--duration) var(--ease-out);
  white-space: nowrap;
  text-decoration: none;
}

/* Primary — dark fill */
.btn--primary {
  background: var(--color-ink);
  color: var(--color-white);
  border-color: var(--color-ink);
}

.btn--primary:hover {
  background: var(--color-ink-soft);
  border-color: var(--color-ink-soft);
}

/* Ghost — border only */
.btn--ghost {
  background: transparent;
  color: var(--color-ink);
  border-color: var(--color-line);
}

.btn--ghost:hover {
  border-color: var(--color-mid);
  background: var(--color-surface);
}

/* Text — inline, no chrome */
.btn--text {
  background: transparent;
  color: var(--color-mid);
  padding-inline: 0;
  border: none;
}

.btn--text:hover {
  color: var(--color-ink);
}

/* --- Links --- */

.link {
  color: var(--color-ink);
  text-decoration: underline;
  text-decoration-color: var(--color-line);
  text-underline-offset: 3px;
  transition: text-decoration-color var(--duration) var(--ease-out),
              color var(--duration) var(--ease-out);
}

.link:hover {
  text-decoration-color: var(--color-ink);
}

/* --- Tag / Chip --- */

.tag {
  display: inline-flex;
  align-items: center;
  font-size: var(--text-xs);
  font-weight: var(--weight-medium);
  letter-spacing: var(--tracking-wide);
  text-transform: uppercase;
  color: var(--color-mid);
  background: var(--color-surface);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  padding: var(--space-1) var(--space-3);
  transition: color var(--duration) var(--ease-out),
              border-color var(--duration) var(--ease-out);
}

.tag:hover {
  color: var(--color-ink);
  border-color: var(--color-mid);
}

/* --- Badge --- */

.badge {
  display: inline-flex;
  align-items: center;
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-wide);
  text-transform: uppercase;
  color: var(--color-white);
  background: var(--color-ink);
  border-radius: var(--radius-sm);
  padding: 2px var(--space-2);
}


/* ============================================================
   13. FOOTER
   Minimal — Vercel-style ground floor
   ============================================================ */

.site-footer {
  border-top: 1px solid var(--color-line);
  padding-block: var(--space-12);
  margin-block-start: var(--space-32);
}

.site-footer__inner {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: var(--space-8);
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--space-8);
}

.site-footer__brand {}

.site-footer__logo {
  font-size: var(--text-base);
  font-weight: var(--weight-bold);
  letter-spacing: var(--tracking-tight);
  color: var(--color-ink);
  margin-bottom: var(--space-2);
}

.site-footer__tagline {
  font-size: var(--text-sm);
  color: var(--color-muted);
  max-width: 32ch;
}

.site-footer__nav {
  display: flex;
  gap: var(--space-16);
}

.site-footer__col {}

.site-footer__col-title {
  font-size: var(--text-xs);
  font-weight: var(--weight-semibold);
  letter-spacing: var(--tracking-widest);
  text-transform: uppercase;
  color: var(--color-muted);
  margin-bottom: var(--space-4);
}

.site-footer__col ul {
  display: flex;
  flex-direction: column;
  gap: var(--space-3);
}

.site-footer__col a {
  font-size: var(--text-sm);
  color: var(--color-mid);
  transition: color var(--duration) var(--ease-out);
}

.site-footer__col a:hover {
  color: var(--color-ink);
}

.site-footer__bottom {
  display: flex;
  align-items: center;
  justify-content: space-between;
  border-top: 1px solid var(--color-line);
  padding-block-start: var(--space-6);
  margin-block-start: var(--space-10);
  max-width: var(--container-xl);
  margin-inline: auto;
  padding-inline: var(--space-8);
}

.site-footer__copy {
  font-size: var(--text-xs);
  color: var(--color-muted);
}

.site-footer__legal {
  display: flex;
  gap: var(--space-6);
}

.site-footer__legal a {
  font-size: var(--text-xs);
  color: var(--color-muted);
  transition: color var(--duration) var(--ease-out);
}

.site-footer__legal a:hover {
  color: var(--color-mid);
}


/* ============================================================
   14. UTILITIES
   ============================================================ */

.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;
}

.text-center  { text-align: center; }
.text-right   { text-align: right; }
.text-muted   { color: var(--color-muted); }
.text-mid     { color: var(--color-mid); }
.text-ink     { color: var(--color-ink); }

.w-full { width: 100%; }

.mt-auto { margin-block-start: auto; }


/* ============================================================
   15. RESPONSIVE
   Mobile-first breakpoints — no sidebars, stack everything
   ============================================================ */

@media (max-width: 1024px) {
  .featured__inner {
    grid-template-columns: 1fr;
  }

  .featured__image {
    order: -1;
  }

  .keys-grid {
    grid-template-columns: 1fr;
    gap: var(--space-6);
  }

  .site-footer__inner {
    flex-direction: column;
    gap: var(--space-10);
  }

  .site-footer__nav {
    gap: var(--space-10);
  }
}

@media (max-width: 768px) {
  :root {
    --header-height: 52px;
  }

  .container {
    padding-inline: var(--space-5);
  }

  .section {
    padding-block: var(--space-16);
  }

  .section--lg {
    padding-block: var(--space-20);
  }

  .article-row {
    grid-template-columns: 1fr;
    gap: var(--space-2);
  }

  .grid-2,
  .grid-3 {
    grid-template-columns: 1fr;
  }

  .card-grid {
    grid-template-columns: 1fr;
  }

  .site-nav {
    gap: var(--space-5);
  }

  .site-footer__nav {
    flex-direction: column;
    gap: var(--space-8);
  }

  .site-footer__bottom {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--space-4);
  }

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

@media (max-width: 480px) {
  .site-nav__link:not(.site-nav__cta) {
    display: none;
  }
}


/* ============================================================
   16. FOCUS / ACCESSIBILITY
   Visible focus ring — product quality, not afterthought
   ============================================================ */

:focus-visible {
  outline: 2px solid var(--color-ink);
  outline-offset: 3px;
  border-radius: var(--radius-sm);
}

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