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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
  color: #333;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background: #f5f7fa;
}

.container { max-width: 1100px; margin: 0 auto; padding: 0 20px; }

/* Header */
.site-header {
  background: #fff;
  border-bottom: 1px solid #e2e8f0;
  padding: 16px 0;
}
.site-header .container { display: flex; align-items: center; justify-content: space-between; }
.logo { font-size: 1.25rem; font-weight: 700; color: #1a56db; text-decoration: none; }
.site-header nav a { color: #64748b; text-decoration: none; font-size: 0.9rem; }
.site-header nav a:hover { color: #1a56db; }

/* Footer */
.site-footer {
  margin-top: auto;
  padding: 24px 0;
  text-align: center;
  color: #94a3b8;
  font-size: 0.85rem;
}

/* Main content */
main { flex: 1; padding: 32px 0; }
h1 { margin-bottom: 24px; font-size: 1.75rem; }

/* Course grid */
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 24px;
}

.course-card {
  background: #fff;
  border-radius: 12px;
  overflow: hidden;
  text-decoration: none;
  color: inherit;
  border: 1px solid #e2e8f0;
  transition: box-shadow 0.2s, transform 0.2s;
}
.course-card:hover {
  box-shadow: 0 4px 12px rgba(0,0,0,0.08);
  transform: translateY(-2px);
}

.course-cover { height: 160px; background: #e2e8f0; overflow: hidden; }
.course-cover img { width: 100%; height: 100%; object-fit: cover; }
.cover-placeholder {
  height: 100%;
  display: flex; align-items: center; justify-content: center;
  font-size: 3rem; font-weight: 700; color: #94a3b8;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: #fff;
}

.course-info { padding: 16px; }
.course-info h3 { margin-bottom: 8px; font-size: 1.1rem; }
.course-info p { color: #64748b; font-size: 0.9rem; margin-bottom: 12px; }

.badge {
  display: inline-block; padding: 3px 10px;
  border-radius: 12px; font-size: 0.75rem; font-weight: 500;
}
.badge-public { background: #dcfce7; color: #166534; }
.badge-invite, .badge-invite_code { background: #fef3c7; color: #92400e; }
.badge-private { background: #fee2e2; color: #991b1b; }

.empty { text-align: center; color: #94a3b8; padding: 48px; }

/* Invite code page */
.invite-card {
  max-width: 480px;
  margin: 60px auto;
  background: #fff;
  border-radius: 12px;
  padding: 40px;
  text-align: center;
  border: 1px solid #e2e8f0;
}
.invite-card h2 { margin-bottom: 12px; }
.invite-card p { color: #64748b; margin-bottom: 8px; }
.invite-hint { color: #92400e; font-size: 0.9rem; margin-bottom: 24px !important; }

.invite-form { display: flex; gap: 8px; }
.invite-form input {
  flex: 1; padding: 10px 14px;
  border: 1px solid #d1d5db; border-radius: 8px; font-size: 1rem;
}
.invite-form button, .login-card button {
  padding: 10px 24px;
  background: #1a56db; color: #fff; border: none; border-radius: 8px;
  font-size: 1rem; cursor: pointer;
}
.invite-form button:hover, .login-card button:hover { background: #1e40af; }

.error-msg { color: #dc2626; margin-top: 12px; font-size: 0.9rem; }

/* Login */
.login-card {
  max-width: 400px;
  margin: 60px auto;
  background: #fff;
  border-radius: 12px;
  padding: 40px;
  border: 1px solid #e2e8f0;
}
.login-card h2 { text-align: center; margin-bottom: 24px; }
.form-group { margin-bottom: 16px; }
.form-group label { display: block; margin-bottom: 6px; font-weight: 500; font-size: 0.9rem; }
.form-group input, .form-group select, .form-group textarea {
  width: 100%; padding: 10px 14px;
  border: 1px solid #d1d5db; border-radius: 8px; font-size: 1rem;
}
.login-card button { width: 100%; margin-top: 8px; }