:root {
  /* Light Theme (Default) */
  --bg-body: #ffffff;
  --bg-card: #ffffff;
  --text-primary: #1d1d1f;
  --text-secondary: #86868b;
  --border-color: #d2d2d7;
  --border-light: #e5e5e5;
  --accent-color: #007aff;
  --accent-hover: #0062cc;
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 6px rgba(0,0,0,0.05);
  --radius-md: 12px;
  --radius-lg: 16px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg-body: #1c1c1e;
    --bg-card: #2c2c2e;
    --text-primary: #f5f5f7;
    --text-secondary: #aeaeb2;
    --border-color: #48484a;
    --border-light: #38383a;
    --accent-color: #0a84ff;
    --accent-hover: #409cff;
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.2);
    --shadow-md: 0 4px 12px rgba(0,0,0,0.3);
  }
}

* { box-sizing: border-box; }

body { 
  font-family: -apple-system, BlinkMacSystemFont, "SF Pro Text", "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background-color: var(--bg-body);
  color: var(--text-primary);
  margin: 0; 
  padding: 0; 
  line-height: 1.6;
  transition: background-color 0.3s, color 0.3s;
}

.container {
  max-width: 800px;
  margin: 0 auto;
  padding: 40px 20px;
}

header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 40px;
  padding-bottom: 20px;
  border-bottom: 1px solid var(--border-light);
}

.header-left {
  display: flex;
  align-items: center;
  gap: 16px;
}

.lang-switch {
  display: flex;
  background: var(--bg-card);
  border: 1px solid var(--border-light);
  border-radius: 8px;
  padding: 2px;
}

.lang-btn {
  border: none;
  background: transparent;
  padding: 4px 12px;
  border-radius: 6px;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-secondary);
  cursor: pointer;
  transition: all 0.2s;
}

.lang-btn.active {
  background: var(--bg-hover, #f0f0f2);
  color: var(--text-primary);
  font-weight: 600;
}

@media (prefers-color-scheme: dark) {
  .lang-btn.active {
    background: #3a3a3c;
  }
}

.lang-btn:hover:not(.active) {
  color: var(--text-primary);
}

.logo-icon {
  width: 48px;
  height: 48px;
  background: linear-gradient(135deg, var(--accent-color), #5ac8fa);
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-size: 20px;
  font-weight: 700;
  box-shadow: 0 4px 8px rgba(0,0,0,0.15);
  user-select: none;
}

h1 { 
  font-size: 32px; 
  font-weight: 700; 
  margin: 0; 
  color: var(--text-primary); 
  letter-spacing: -0.5px;
}

h2 { 
  font-size: 24px; 
  font-weight: 600; 
  margin: 32px 0 16px 0; 
  color: var(--text-primary);
}

h3 {
  font-size: 18px;
  font-weight: 600;
  margin: 24px 0 12px 0;
  color: var(--text-primary);
}

p, li {
  font-size: 16px;
  color: var(--text-secondary);
  margin-bottom: 16px;
}

ul {
  padding-left: 24px;
  margin-bottom: 16px;
}

li {
  margin-bottom: 8px;
}

.card {
  background: var(--bg-card);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  border: 1px solid var(--border-light);
  padding: 32px;
  margin-bottom: 32px;
}

.footer {
  text-align: center;
  margin-top: 60px;
  padding-top: 20px;
  border-top: 1px solid var(--border-light);
  color: var(--text-secondary);
  font-size: 14px;
}

a {
  color: var(--accent-color);
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

.last-updated {
  font-size: 14px;
  color: var(--text-secondary);
  margin-top: 8px;
  margin-bottom: 32px;
}