:root {
  --primary-color: #2563eb;
  --primary-hover: #1d4ed8;
  --secondary-color: #64748b;
  --success-color: #10b981;
  --error-color: #ef4444;
  --warning-color: #f59e0b;
  --bg-color: #f8fafc;
  --card-bg: #ffffff;
  --text-color: #1e293b;
  --text-secondary: #64748b;
  --border-color: #e2e8f0;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Microsoft YaHei", sans-serif;
  line-height: 1.6;
  color: var(--text-color);
  background-color: var(--bg-color);
}

header {
  background-color: var(--card-bg);
  border-bottom: 1px solid var(--border-color);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

nav {
  padding: 1rem 0;
}

.nav-container {
  max-width: 1200px;
  margin: 0 auto;
  padding: 0 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

nav h1 {
  font-size: 1.5rem;
  color: var(--primary-color);
}

nav ul {
  list-style: none;
  display: flex;
  gap: 2rem;
}

nav a {
  text-decoration: none;
  color: var(--text-color);
  font-weight: 500;
  transition: color 0.2s;
}

nav a:hover, nav a.active {
  color: var(--primary-color);
}

main {
  max-width: 1200px;
  margin: 2rem auto;
  padding: 0 2rem;
}

section {
  margin-bottom: 3rem;
}

.hero {
  text-align: center;
  padding: 4rem 2rem;
  background: linear-gradient(135deg, var(--primary-color) 0%, #1d4ed8 100%);
  color: white;
  border-radius: 12px;
  margin-bottom: 3rem;
}

.hero h2 {
  font-size: 2.5rem;
  margin-bottom: 1rem;
}

.hero p {
  font-size: 1.2rem;
  margin-bottom: 2rem;
}

.cta-buttons {
  display: flex;
  gap: 1rem;
  justify-content: center;
}

.btn {
  display: inline-block;
  padding: 0.75rem 2rem;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 600;
  transition: all 0.2s;
  border: none;
  cursor: pointer;
  font-size: 1rem;
}

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

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}

.btn-secondary {
  background-color: transparent;
  color: white;
  border: 2px solid white;
}

.btn-secondary:hover {
  background-color: white;
  color: var(--primary-color);
}

.feature-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: 2rem;
  margin-top: 2rem;
}

.feature-card, .doc-card, .download-item {
  background-color: var(--card-bg);
  padding: 2rem;
  border-radius: 8px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
  transition: transform 0.2s;
}

.feature-card:hover, .download-item:hover {
  transform: translateY(-4px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.15);
}

.feature-card h4 {
  color: var(--primary-color);
  margin-bottom: 0.5rem;
  font-size: 1.2rem;
}

.compatibility ul, .doc-card ul {
  list-style: none;
  padding-left: 0;
}

.compatibility li, .doc-card li {
  padding: 0.5rem 0;
  border-bottom: 1px solid var(--border-color);
}

.downloads-list {
  display: grid;
  gap: 1.5rem;
  margin-top: 2rem;
}

.download-item {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.download-info h4 {
  color: var(--primary-color);
  margin-bottom: 0.5rem;
}

.download-meta {
  font-size: 0.9rem;
  color: var(--text-secondary);
  margin: 0.5rem 0;
}

.download-btn {
  padding: 0.5rem 1.5rem;
  background-color: var(--primary-color);
  color: white;
  border: none;
  border-radius: 6px;
  cursor: pointer;
  font-weight: 600;
  transition: background-color 0.2s;
}

.download-btn:hover {
  background-color: var(--primary-hover);
}

.loading {
  text-align: center;
  padding: 2rem;
  color: var(--text-secondary);
}

.error {
  background-color: #fef2f2;
  color: var(--error-color);
  padding: 1rem;
  border-radius: 6px;
  border-left: 4px solid var(--error-color);
  margin: 1rem 0;
}

.success {
  background-color: #f0fdf4;
  color: var(--success-color);
  padding: 1rem;
  border-radius: 6px;
  border-left: 4px solid var(--success-color);
  margin: 1rem 0;
}

.warning {
  background-color: #fffbeb;
  color: #92400e;
  padding: 1.5rem;
  border-radius: 6px;
  border-left: 4px solid var(--warning-color);
  margin: 2rem 0;
}

.auth-form, .upload-form {
  max-width: 500px;
  margin: 2rem auto;
  padding: 2rem;
  background-color: var(--card-bg);
  border-radius: 8px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.form-group {
  margin-bottom: 1.5rem;
}

.form-group label {
  display: block;
  margin-bottom: 0.5rem;
  font-weight: 600;
  color: var(--text-color);
}

.form-group input,
.form-group select,
.form-group textarea {
  width: 100%;
  padding: 0.75rem;
  border: 1px solid var(--border-color);
  border-radius: 6px;
  font-size: 1rem;
  font-family: inherit;
}

.form-group input:focus,
.form-group select:focus,
.form-group textarea:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.1);
}

.form-group small {
  display: block;
  margin-top: 0.25rem;
  color: var(--text-secondary);
  font-size: 0.875rem;
}

.progress-bar {
  width: 100%;
  height: 24px;
  background-color: var(--border-color);
  border-radius: 12px;
  overflow: hidden;
  margin: 1rem 0;
}

.progress-fill {
  height: 100%;
  background-color: var(--primary-color);
  transition: width 0.3s;
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-weight: 600;
  font-size: 0.875rem;
}

.logout-btn {
  text-align: center;
  margin-top: 2rem;
}

footer {
  background-color: var(--card-bg);
  border-top: 1px solid var(--border-color);
  padding: 2rem 0;
  text-align: center;
  color: var(--text-secondary);
  margin-top: 4rem;
}

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

footer a:hover {
  text-decoration: underline;
}

@media (max-width: 768px) {
  .nav-container {
    flex-direction: column;
    gap: 1rem;
  }

  nav ul {
    gap: 1rem;
  }

  .hero h2 {
    font-size: 1.8rem;
  }

  .feature-grid {
    grid-template-columns: 1fr;
  }

  .download-item {
    flex-direction: column;
    align-items: flex-start;
    gap: 1rem;
  }
}