:root {
  --bg: #ffffff;
  --surface: #f7f7f7;
  --surface-2: #fafafa;
  --text-primary: #1c1c1e;
  --text-secondary: #6c6c70;
  --text-tertiary: #8e8e93;
  --border: #e5e5ea;
  --accent: #ff385c;
  --link: #0a84ff;
  --code-bg: #f2f2f7;
  --shadow: 0 1px 3px rgba(0, 0, 0, 0.04), 0 4px 12px rgba(0, 0, 0, 0.04);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #000000;
    --surface: #1c1c1e;
    --surface-2: #2c2c2e;
    --text-primary: #f5f5f7;
    --text-secondary: #a1a1a6;
    --text-tertiary: #6e6e73;
    --border: #2c2c2e;
    --accent: #ff5a7a;
    --link: #0a84ff;
    --code-bg: #1c1c1e;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.4), 0 4px 12px rgba(0, 0, 0, 0.4);
  }
}

* {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text-primary);
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "SF Pro Display",
    "Helvetica Neue", "Segoe UI", system-ui, sans-serif;
  font-size: 17px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 48px 24px 96px;
}

.site-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 20px 24px;
  border-bottom: 1px solid var(--border);
  background: var(--bg);
  position: sticky;
  top: 0;
  z-index: 10;
  backdrop-filter: saturate(180%) blur(20px);
  -webkit-backdrop-filter: saturate(180%) blur(20px);
  background: rgba(255, 255, 255, 0.8);
}

@media (prefers-color-scheme: dark) {
  .site-header {
    background: rgba(0, 0, 0, 0.7);
  }
}

.site-header__inner {
  max-width: 900px;
  margin: 0 auto;
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand {
  font-weight: 600;
  font-size: 18px;
  letter-spacing: -0.01em;
  color: var(--text-primary);
  text-decoration: none;
}

.brand__accent {
  color: var(--accent);
}

.lang-toggle {
  display: inline-flex;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 3px;
  gap: 2px;
}

.lang-toggle__btn {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--text-secondary);
  font: inherit;
  font-size: 13px;
  font-weight: 500;
  letter-spacing: 0.02em;
  padding: 6px 14px;
  border-radius: 999px;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease;
}

.lang-toggle__btn:hover {
  color: var(--text-primary);
}

.lang-toggle__btn.is-active {
  background: var(--bg);
  color: var(--text-primary);
  box-shadow: 0 1px 2px rgba(0, 0, 0, 0.06);
}

@media (prefers-color-scheme: dark) {
  .lang-toggle__btn.is-active {
    background: var(--surface-2);
  }
}

h1, h2, h3, h4 {
  color: var(--text-primary);
  letter-spacing: -0.022em;
  line-height: 1.2;
  font-weight: 600;
}

h1 {
  font-size: 44px;
  margin: 0 0 16px;
  letter-spacing: -0.03em;
}

h2 {
  font-size: 28px;
  margin: 56px 0 16px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
}

h2:first-of-type {
  border-top: 0;
  padding-top: 0;
  margin-top: 32px;
}

h3 {
  font-size: 21px;
  margin: 32px 0 12px;
}

h4 {
  font-size: 17px;
  margin: 24px 0 8px;
}

p {
  margin: 0 0 16px;
  color: var(--text-primary);
}

a {
  color: var(--link);
  text-decoration: none;
  transition: opacity 0.15s ease;
}

a:hover {
  opacity: 0.7;
  text-decoration: underline;
}

ul, ol {
  margin: 0 0 16px;
  padding-left: 24px;
}

li {
  margin-bottom: 6px;
}

strong {
  font-weight: 600;
}

table {
  width: 100%;
  border-collapse: collapse;
  margin: 16px 0 24px;
  font-size: 15px;
  border: 1px solid var(--border);
  border-radius: 12px;
  overflow: hidden;
}

th, td {
  text-align: left;
  padding: 12px 16px;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

th {
  background: var(--surface);
  font-weight: 600;
  color: var(--text-primary);
  font-size: 14px;
  letter-spacing: 0.01em;
}

tr:last-child td {
  border-bottom: 0;
}

blockquote {
  margin: 16px 0;
  padding: 14px 18px;
  background: var(--surface);
  border-left: 3px solid var(--accent);
  border-radius: 8px;
  color: var(--text-secondary);
  font-size: 15px;
}

blockquote p:last-child {
  margin-bottom: 0;
}

code {
  font-family: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
  font-size: 14px;
  background: var(--code-bg);
  padding: 2px 6px;
  border-radius: 4px;
}

hr {
  border: 0;
  border-top: 1px solid var(--border);
  margin: 48px 0;
}

.meta {
  color: var(--text-secondary);
  font-size: 15px;
  margin-bottom: 32px;
}

.meta strong {
  color: var(--text-primary);
}

.lang-section {
  display: none;
}

.lang-section.is-active {
  display: block;
}

.hero {
  text-align: center;
  padding: 80px 0 48px;
}

.hero__title {
  font-size: 56px;
  font-weight: 700;
  letter-spacing: -0.035em;
  margin: 0 0 12px;
  line-height: 1.05;
}

.hero__subtitle {
  font-size: 21px;
  color: var(--text-secondary);
  margin: 0 0 32px;
  font-weight: 400;
  letter-spacing: -0.01em;
}

.hero__tagline {
  font-size: 17px;
  color: var(--text-secondary);
  max-width: 560px;
  margin: 0 auto 40px;
}

.cta-row {
  display: flex;
  gap: 12px;
  justify-content: center;
  flex-wrap: wrap;
  margin-top: 8px;
}

.btn {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  padding: 12px 22px;
  border-radius: 999px;
  font-weight: 500;
  font-size: 15px;
  text-decoration: none;
  transition: opacity 0.15s ease, transform 0.15s ease;
}

.btn:hover {
  opacity: 0.85;
  text-decoration: none;
}

.btn:active {
  transform: scale(0.98);
}

.btn--primary {
  background: var(--text-primary);
  color: var(--bg);
}

.btn--secondary {
  background: var(--surface);
  color: var(--text-primary);
  border: 1px solid var(--border);
}

.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 16px;
  margin-top: 64px;
}

.feature {
  padding: 24px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
}

.feature__title {
  font-size: 17px;
  font-weight: 600;
  margin: 0 0 8px;
}

.feature__desc {
  font-size: 15px;
  color: var(--text-secondary);
  margin: 0;
}

.footer {
  max-width: 900px;
  margin: 80px auto 0;
  padding: 32px 24px;
  border-top: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 16px;
  color: var(--text-tertiary);
  font-size: 14px;
}

.footer a {
  color: var(--text-secondary);
}

@media (max-width: 640px) {
  .container {
    padding: 32px 20px 64px;
  }

  h1 { font-size: 34px; }
  h2 { font-size: 24px; margin-top: 40px; }
  h3 { font-size: 19px; }

  .hero__title { font-size: 40px; }
  .hero__subtitle { font-size: 18px; }
  .hero { padding: 48px 0 32px; }

  table {
    font-size: 14px;
    display: block;
    overflow-x: auto;
    -webkit-overflow-scrolling: touch;
  }

  th, td {
    padding: 10px 12px;
  }

  .site-header {
    padding: 14px 20px;
  }

  body {
    font-size: 16px;
  }
}