:root {
  --bg-color: #f8fafc;
  --text-main: #0f172a;
  --text-muted: #475569;
  --card-bg: #ffffff;
  --primary: #3b82f6;
  --primary-hover: #2563eb;
  --border: #e2e8f0;
}

* {
  box-sizing: border-box;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
  background-color: var(--bg-color);
  color: var(--text-main);
  line-height: 1.6;
  margin: 0;
  padding: 20px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.container {
  max-width: 640px;
  margin: 40px auto;
}

.header {
  text-align: center;
  margin-bottom: 32px;
}

.header h1 {
  font-size: 2rem;
  font-weight: 800;
  letter-spacing: -0.025em;
  margin-bottom: 8px;
  color: var(--text-main);
}

.header p {
  font-size: 1.125rem;
  color: var(--text-muted);
  margin: 0;
}

.card {
  background: var(--card-bg);
  border-radius: 16px;
  padding: 32px;
  box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.05), 0 2px 4px -1px rgba(0, 0, 0, 0.03);
  margin-bottom: 24px;
  border: 1px solid var(--border);
}

h1, h2, h3 {
  margin-top: 0;
  color: var(--text-main);
  font-weight: 700;
  letter-spacing: -0.025em;
}

h2 {
  font-size: 1.5rem;
  margin-bottom: 16px;
}

h3 {
  font-size: 1.125rem;
  margin-bottom: 8px;
  margin-top: 24px;
}

p {
  color: var(--text-muted);
  margin-top: 0;
  margin-bottom: 16px;
}

ul {
  color: var(--text-muted);
  margin-top: 0;
  margin-bottom: 16px;
  padding-left: 20px;
}

li {
  margin-bottom: 8px;
}

a {
  color: var(--primary);
  text-decoration: none;
  font-weight: 500;
  transition: color 0.15s ease;
}

a:hover {
  text-decoration: underline;
  color: var(--primary-hover);
}

.nav-back {
  display: inline-flex;
  align-items: center;
  margin-bottom: 24px;
  font-size: 0.95rem;
  color: var(--text-muted);
}

.nav-back::before {
  content: "←";
  margin-right: 6px;
}

.nav-back:hover {
  color: var(--text-main);
  text-decoration: none;
}

.footer {
  text-align: center;
  margin-top: 40px;
  padding-top: 24px;
  border-top: 1px solid var(--border);
  font-size: 0.875rem;
  color: var(--text-muted);
}

.footer-links {
  display: flex;
  justify-content: center;
  gap: 24px;
  margin-bottom: 16px;
}

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

.footer-links a:hover {
  color: var(--text-main);
}

@media (max-width: 640px) {
  .container {
    margin: 20px auto;
  }
  .card {
    padding: 24px;
  }
  .header h1 {
    font-size: 1.75rem;
  }
}