/* ============================================
   DiffBetween.net — Stylesheet
   System font stack for instant rendering.
   No external dependencies.
   ============================================ */

/* --- Reset & Base --- */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  /* Palette */
  --c-bg:        #FAFBFC;
  --c-surface:   #FFFFFF;
  --c-border:    #E2E8F0;
  --c-text:      #1E293B;
  --c-text-mid:  #475569;
  --c-text-soft: #64748B;
  --c-primary:   #2563EB;
  --c-primary-h: #1D4ED8;
  --c-accent-a:  #DBEAFE;
  --c-accent-b:  #F1F5F9;
  --c-vs:        #EF4444;
  --c-badge-tech:    #EFF6FF;
  --c-badge-finance: #F0FDF4;
  --c-badge-science: #FFF7ED;
  --c-icon-tech:     #2563EB;
  --c-icon-finance:  #16A34A;
  --c-icon-science:  #EA580C;

  /* Spacing */
  --sp-xs: 0.25rem;
  --sp-sm: 0.5rem;
  --sp-md: 1rem;
  --sp-lg: 1.5rem;
  --sp-xl: 2.5rem;
  --sp-2xl: 4rem;

  /* Typography */
  --font: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Helvetica Neue", Arial, sans-serif;
  --font-mono: "SF Mono", "Fira Code", "Fira Mono", "Roboto Mono", monospace;
  --fs-hero: clamp(2rem, 5vw, 3.25rem);
  --fs-h2: clamp(1.35rem, 3vw, 1.75rem);
  --fs-h3: 1.1rem;
  --fs-body: 1rem;
  --fs-sm: 0.875rem;
  --fs-xs: 0.8rem;

  /* Misc */
  --radius: 10px;
  --radius-sm: 6px;
  --shadow-sm: 0 1px 3px rgba(15,23,42,0.06);
  --shadow-md: 0 4px 12px rgba(15,23,42,0.08);
  --shadow-lg: 0 8px 30px rgba(15,23,42,0.1);
  --transition: 0.2s ease;
}

html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  font-family: var(--font);
  font-size: var(--fs-body);
  color: var(--c-text);
  background: var(--c-bg);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
a { color: var(--c-primary); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--c-primary-h); }
ul { list-style: none; }
img { max-width: 100%; display: block; }

.container {
  width: 100%;
  max-width: 1120px;
  margin: 0 auto;
  padding: 0 var(--sp-lg);
}

/* --- Header --- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--c-border);
}
.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 60px;
}
.logo {
  display: flex;
  align-items: center;
  gap: var(--sp-sm);
  font-weight: 700;
  font-size: 1.15rem;
  color: var(--c-text);
}
.logo:hover { color: var(--c-text); }
.logo-accent { color: var(--c-primary); }
.nav-list { display: flex; gap: var(--sp-lg); }
.nav-link {
  font-size: var(--fs-sm);
  font-weight: 500;
  color: var(--c-text-mid);
  padding: var(--sp-xs) 0;
  position: relative;
}
.nav-link::after {
  content: '';
  position: absolute;
  bottom: -2px; left: 0;
  width: 0; height: 2px;
  background: var(--c-primary);
  border-radius: 1px;
  transition: width var(--transition);
}
.nav-link:hover { color: var(--c-primary); }
.nav-link:hover::after { width: 100%; }

.mobile-menu-btn { display: none; background: none; border: none; cursor: pointer; color: var(--c-text); padding: var(--sp-xs); }

/* --- Hero --- */
.hero {
  padding: var(--sp-2xl) 0 var(--sp-xl);
  text-align: center;
  background:
    radial-gradient(ellipse 80% 50% at 50% -20%, rgba(37,99,235,0.07), transparent),
    var(--c-bg);
}
.hero-title {
  font-size: var(--fs-hero);
  font-weight: 800;
  line-height: 1.15;
  letter-spacing: -0.03em;
  color: var(--c-text);
}
.hero-highlight {
  background: linear-gradient(135deg, var(--c-primary) 0%, #7C3AED 100%);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.hero-sub {
  margin-top: var(--sp-md);
  font-size: clamp(1rem, 2vw, 1.2rem);
  color: var(--c-text-mid);
  max-width: 540px;
  margin-left: auto;
  margin-right: auto;
}

/* Search */
.search-box {
  position: relative;
  max-width: 560px;
  margin: var(--sp-xl) auto 0;
  display: flex;
  align-items: center;
  background: var(--c-surface);
  border: 1.5px solid var(--c-border);
  border-radius: 50px;
  overflow: hidden;
  box-shadow: var(--shadow-md);
  transition: border-color var(--transition), box-shadow var(--transition);
}
.search-box:focus-within {
  border-color: var(--c-primary);
  box-shadow: 0 0 0 3px rgba(37,99,235,0.12), var(--shadow-md);
}
.search-icon {
  position: absolute;
  left: 18px;
  color: var(--c-text-soft);
  pointer-events: none;
  flex-shrink: 0;
}
.search-input {
  flex: 1;
  border: none;
  background: transparent;
  padding: 14px 14px 14px 48px;
  font-size: var(--fs-body);
  font-family: var(--font);
  color: var(--c-text);
  outline: none;
  min-width: 0;
}
.search-input::placeholder { color: var(--c-text-soft); }
.search-btn {
  flex-shrink: 0;
  background: var(--c-primary);
  color: #fff;
  border: none;
  padding: 12px 24px;
  margin: 4px;
  border-radius: 50px;
  font-family: var(--font);
  font-size: var(--fs-sm);
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition);
}
.search-btn:hover { background: var(--c-primary-h); }

/* Tags */
.hero-tags {
  margin-top: var(--sp-lg);
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--sp-sm);
  font-size: var(--fs-sm);
}
.tag-label { color: var(--c-text-soft); font-weight: 500; padding: 4px 0; }
.tag {
  display: inline-block;
  background: var(--c-accent-a);
  color: var(--c-primary);
  padding: 5px 14px;
  border-radius: 50px;
  font-weight: 500;
  transition: background var(--transition), color var(--transition);
}
.tag:hover { background: var(--c-primary); color: #fff; }

/* --- Section Titles --- */
.section-title {
  font-size: var(--fs-h2);
  font-weight: 700;
  text-align: center;
  letter-spacing: -0.02em;
  margin-bottom: var(--sp-xl);
}

/* --- How It Works / Features --- */
.how-it-works {
  padding: var(--sp-2xl) 0;
  background: var(--c-surface);
  border-top: 1px solid var(--c-border);
  border-bottom: 1px solid var(--c-border);
}
.features-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-lg);
}
.feature-card {
  text-align: center;
  padding: var(--sp-xl) var(--sp-lg);
}
.feature-icon {
  width: 56px; height: 56px;
  margin: 0 auto var(--sp-md);
  display: flex;
  align-items: center;
  justify-content: center;
  background: var(--c-accent-a);
  color: var(--c-primary);
  border-radius: 14px;
}
.feature-title {
  font-size: var(--fs-h3);
  font-weight: 700;
  margin-bottom: var(--sp-sm);
}
.feature-desc {
  color: var(--c-text-mid);
  font-size: var(--fs-sm);
  line-height: 1.6;
}

/* --- Category Sections --- */
.category-section {
  padding: var(--sp-2xl) 0 var(--sp-xl);
}
.category-section:nth-child(even) {
  background: var(--c-surface);
  border-top: 1px solid var(--c-border);
  border-bottom: 1px solid var(--c-border);
}
.category-header {
  display: flex;
  align-items: center;
  gap: var(--sp-md);
  margin-bottom: var(--sp-xl);
  flex-wrap: wrap;
}
.category-badge {
  width: 48px; height: 48px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 12px;
  flex-shrink: 0;
}
.badge-tech    { background: var(--c-badge-tech);    color: var(--c-icon-tech); }
.badge-finance { background: var(--c-badge-finance); color: var(--c-icon-finance); }
.badge-science { background: var(--c-badge-science); color: var(--c-icon-science); }
.category-title {
  font-size: var(--fs-h2);
  font-weight: 700;
  letter-spacing: -0.02em;
}
.category-desc {
  font-size: var(--fs-sm);
  color: var(--c-text-soft);
  margin-top: 2px;
}
.category-all {
  margin-left: auto;
  font-size: var(--fs-sm);
  font-weight: 600;
  white-space: nowrap;
}

/* --- Comparison Cards --- */
.comparison-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--sp-md);
}
.comparison-card {
  display: flex;
  flex-direction: column;
  align-items: center;
  text-align: center;
  background: var(--c-surface);
  border: 1px solid var(--c-border);
  border-radius: var(--radius);
  padding: var(--sp-lg) var(--sp-md);
  transition: border-color var(--transition), box-shadow var(--transition), transform var(--transition);
  color: var(--c-text);
  position: relative;
}
.comparison-card:hover {
  border-color: var(--c-primary);
  box-shadow: var(--shadow-md);
  transform: translateY(-2px);
  color: var(--c-text);
}
.card-a, .card-b {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: -0.01em;
}
.card-a { color: var(--c-primary); }
.card-b { color: var(--c-text); }
.card-vs {
  font-size: var(--fs-xs);
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--c-vs);
  margin: 6px 0;
}
.card-snippet {
  font-size: var(--fs-sm);
  color: var(--c-text-mid);
  line-height: 1.55;
  margin-top: var(--sp-sm);
}

/* --- CTA Section --- */
.cta-section {
  padding: var(--sp-2xl) 0;
}
.cta-box {
  background: var(--c-text);
  color: #fff;
  border-radius: var(--radius);
  padding: var(--sp-2xl) var(--sp-xl);
  text-align: center;
  max-width: 680px;
  margin: 0 auto;
}
.cta-title {
  font-size: var(--fs-h2);
  font-weight: 700;
  letter-spacing: -0.02em;
}
.cta-desc {
  margin-top: var(--sp-sm);
  color: #94A3B8;
  font-size: var(--fs-sm);
}
.cta-form {
  margin-top: var(--sp-lg);
  display: flex;
  max-width: 420px;
  margin-left: auto;
  margin-right: auto;
  gap: var(--sp-sm);
}
.cta-input {
  flex: 1;
  padding: 12px 16px;
  border: 1.5px solid #334155;
  border-radius: 50px;
  background: #1E293B;
  color: #fff;
  font-family: var(--font);
  font-size: var(--fs-sm);
  outline: none;
  transition: border-color var(--transition);
  min-width: 0;
}
.cta-input::placeholder { color: #64748B; }
.cta-input:focus { border-color: var(--c-primary); }
.cta-btn {
  flex-shrink: 0;
  background: var(--c-primary);
  color: #fff;
  border: none;
  padding: 12px 24px;
  border-radius: 50px;
  font-family: var(--font);
  font-size: var(--fs-sm);
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition);
}
.cta-btn:hover { background: var(--c-primary-h); }

/* --- Footer --- */
.site-footer {
  background: var(--c-surface);
  border-top: 1px solid var(--c-border);
  padding: var(--sp-2xl) 0 var(--sp-lg);
  color: var(--c-text-mid);
  font-size: var(--fs-sm);
}
.footer-inner {
  display: flex;
  gap: var(--sp-2xl);
  justify-content: space-between;
  flex-wrap: wrap;
}
.footer-brand { max-width: 260px; }
.logo-footer .logo-text { font-size: 1rem; }
.footer-tagline { margin-top: var(--sp-sm); color: var(--c-text-soft); }
.footer-nav {
  display: flex;
  gap: var(--sp-2xl);
}
.footer-heading {
  font-size: var(--fs-sm);
  font-weight: 700;
  color: var(--c-text);
  margin-bottom: var(--sp-md);
  text-transform: uppercase;
  letter-spacing: 0.04em;
}
.footer-col ul { display: flex; flex-direction: column; gap: var(--sp-sm); }
.footer-col a { color: var(--c-text-mid); }
.footer-col a:hover { color: var(--c-primary); }
.footer-copy {
  margin-top: var(--sp-xl);
  padding-top: var(--sp-lg);
  border-top: 1px solid var(--c-border);
  text-align: center;
  color: var(--c-text-soft);
  font-size: var(--fs-xs);
}

/* ==========================================
   RESPONSIVE
   ========================================== */

@media (max-width: 900px) {
  .features-grid { grid-template-columns: 1fr; gap: 0; }
  .feature-card { padding: var(--sp-lg); }
  .comparison-grid { grid-template-columns: repeat(2, 1fr); }
}

@media (max-width: 640px) {
  .container { padding: 0 var(--sp-md); }

  /* Header */
  .main-nav { display: none; }
  .main-nav.is-open {
    display: flex;
    position: absolute;
    top: 60px; left: 0; right: 0;
    background: var(--c-surface);
    border-bottom: 1px solid var(--c-border);
    padding: var(--sp-md) var(--sp-lg);
    box-shadow: var(--shadow-md);
  }
  .main-nav.is-open .nav-list {
    flex-direction: column;
    gap: var(--sp-md);
    width: 100%;
  }
  .mobile-menu-btn { display: block; }

  /* Hero */
  .hero { padding: var(--sp-xl) 0; }
  .hero-title { font-size: clamp(1.65rem, 6vw, 2.2rem); }
  .search-box { border-radius: var(--radius); }
  .search-btn { border-radius: var(--radius-sm); padding: 12px 18px; }
  .search-input { padding: 12px 12px 12px 44px; }

  /* Cards */
  .comparison-grid { grid-template-columns: 1fr; }
  .comparison-card {
    flex-direction: row;
    flex-wrap: wrap;
    text-align: left;
    padding: var(--sp-md);
    gap: 0 var(--sp-sm);
  }
  .card-a, .card-vs, .card-b { display: inline; }
  .card-vs { margin: 0 4px; }
  .card-snippet { width: 100%; margin-top: var(--sp-xs); }

  /* Category */
  .category-header { gap: var(--sp-sm); }
  .category-all { margin-left: 0; width: 100%; }

  /* CTA */
  .cta-box { padding: var(--sp-xl) var(--sp-md); }
  .cta-form { flex-direction: column; }

  /* Footer */
  .footer-inner { flex-direction: column; gap: var(--sp-xl); }
  .footer-nav { gap: var(--sp-xl); }
}

/* --- Focus Visible --- */
:focus-visible {
  outline: 2px solid var(--c-primary);
  outline-offset: 2px;
}
button:focus:not(:focus-visible),
a:focus:not(:focus-visible) { outline: none; }

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