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

html {
  scroll-behavior: smooth;
}

body {
  font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
  background: #f5f7fa;
  color: #2c3e50;
  line-height: 1.7;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
}

.container {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 1.25rem;
}

header {
  background: linear-gradient(135deg, #1a3a5c 0%, #0d2137 100%);
  color: #fff;
  padding: 1.5rem 0;
  border-bottom: 3px solid #4fc3f7;
}

.header-inner {
  max-width: 860px;
  margin: 0 auto;
  padding: 0 1.25rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}

.logo a {
  color: #fff;
  text-decoration: none;
  font-size: 1.1rem;
  font-weight: 700;
  letter-spacing: 0.5px;
}

.logo a:hover {
  color: #4fc3f7;
}

.logo span {
  color: #4fc3f7;
}

nav {
  display: flex;
  gap: 0.25rem;
  flex-wrap: wrap;
}

nav a {
  display: inline-block;
  padding: 0.3rem 0.75rem;
  color: #b0c4d8;
  text-decoration: none;
  font-size: 0.85rem;
  border: 1px solid transparent;
  border-radius: 4px;
  transition: all 0.2s;
}

nav a:hover {
  color: #4fc3f7;
  border-color: #4fc3f7;
}

nav a.active {
  color: #4fc3f7;
  border-color: #4fc3f7;
  background: rgba(79, 195, 247, 0.1);
}

main {
  flex: 1;
  padding: 2rem 0 3rem;
}

h1 {
  font-size: 1.8rem;
  font-weight: 800;
  color: #1a3a5c;
  margin-bottom: 1rem;
  line-height: 1.3;
}

h2 {
  font-size: 1.4rem;
  font-weight: 700;
  color: #1a3a5c;
  margin: 2rem 0 1rem;
  line-height: 1.3;
  padding-bottom: 0.3rem;
  border-bottom: 2px solid #e8edf3;
}

h3 {
  font-size: 1.15rem;
  font-weight: 600;
  color: #2c3e50;
  margin: 1.5rem 0 0.75rem;
}

p {
  margin-bottom: 1rem;
  font-size: 1rem;
  color: #444;
}

a {
  color: #1976d2;
  text-decoration: none;
  transition: color 0.2s;
}

a:hover {
  color: #0d47a1;
  text-decoration: underline;
}

ul, ol {
  margin: 0 0 1.25rem 1.5rem;
  font-size: 1rem;
  color: #444;
}

li {
  margin-bottom: 0.4rem;
}

strong {
  color: #1a3a5c;
}

blockquote {
  margin: 1.25rem 0;
  padding: 1rem 1.25rem;
  background: #e3f2fd;
  border-left: 4px solid #4fc3f7;
  border-radius: 0 6px 6px 0;
  font-size: 0.95rem;
  color: #1a3a5c;
}

.hero {
  text-align: center;
  padding: 2.5rem 0 1.5rem;
}

.hero h1 {
  font-size: 2rem;
  margin-bottom: 0.75rem;
}

.hero p {
  font-size: 1.1rem;
  color: #666;
  max-width: 650px;
  margin: 0 auto 1rem;
}

.article-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.25rem;
  margin-top: 1.5rem;
}

.article-card {
  background: #fff;
  border: 1px solid #e0e6ed;
  border-radius: 10px;
  padding: 1.5rem;
  transition: all 0.25s;
  box-shadow: 0 1px 3px rgba(0,0,0,0.05);
}

.article-card:hover {
  border-color: #4fc3f7;
  box-shadow: 0 4px 15px rgba(79, 195, 247, 0.15);
  transform: translateY(-2px);
}

.article-card h2 {
  border: none;
  margin: 0 0 0.5rem;
  padding: 0;
  font-size: 1.2rem;
}

.article-card h2 a {
  color: #1a3a5c;
  text-decoration: none;
}

.article-card h2 a:hover {
  color: #1976d2;
  text-decoration: underline;
}

.article-card p {
  font-size: 0.9rem;
  color: #666;
  margin-bottom: 0.5rem;
}

.article-meta {
  font-size: 0.8rem;
  color: #999;
  margin-top: 0.5rem;
}

.article-meta a {
  color: #1976d2;
  font-size: 0.8rem;
}

.article-content {
  background: #fff;
  border: 1px solid #e0e6ed;
  border-radius: 10px;
  padding: 2rem;
  box-shadow: 0 1px 3px rgba(0,0,0,0.05);
}

.article-content p {
  font-size: 1.05rem;
  line-height: 1.8;
}

.article-content ul,
.article-content ol {
  font-size: 1.05rem;
  line-height: 1.8;
}

.article-footer {
  margin-top: 2rem;
  padding-top: 1.5rem;
  border-top: 1px solid #e0e6ed;
}

.related-articles {
  margin-top: 2rem;
}

.related-articles h3 {
  margin-bottom: 0.75rem;
}

.related-articles ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.related-articles li {
  margin-bottom: 0.5rem;
}

.related-articles a {
  display: block;
  padding: 0.6rem 1rem;
  background: #f0f4f8;
  border-radius: 6px;
  font-size: 0.95rem;
  transition: all 0.2s;
}

.related-articles a:hover {
  background: #e3f2fd;
  text-decoration: none;
}

.breadcrumbs {
  font-size: 0.85rem;
  color: #999;
  margin-bottom: 1.5rem;
}

.breadcrumbs a {
  color: #1976d2;
}

.breadcrumbs span {
  color: #666;
}

.toc {
  background: #f0f4f8;
  border: 1px solid #e0e6ed;
  border-radius: 8px;
  padding: 1.25rem 1.5rem;
  margin: 1.5rem 0;
}

.toc h3 {
  margin: 0 0 0.75rem;
  font-size: 1rem;
}

.toc ul {
  margin: 0;
  list-style: none;
  padding: 0;
}

.toc li {
  margin-bottom: 0.3rem;
}

.toc a {
  font-size: 0.9rem;
}

.info-box {
  background: #e3f2fd;
  border: 1px solid #bbdefb;
  border-radius: 8px;
  padding: 1rem 1.25rem;
  margin: 1.25rem 0;
}

.info-box strong {
  color: #1565c0;
}

.warning-box {
  background: #fff3e0;
  border: 1px solid #ffe0b2;
  border-radius: 8px;
  padding: 1rem 1.25rem;
  margin: 1.25rem 0;
}

.warning-box strong {
  color: #e65100;
}

footer {
  background: #0d2137;
  color: #8899aa;
  text-align: center;
  padding: 1.5rem 0;
  font-size: 0.85rem;
  margin-top: auto;
}

footer a {
  color: #4fc3f7;
}

footer a:hover {
  color: #81d4fa;
}

@media (min-width: 640px) {
  .article-grid {
    grid-template-columns: 1fr 1fr;
  }
}

@media (min-width: 900px) {
  h1 {
    font-size: 2.2rem;
  }

  .hero h1 {
    font-size: 2.5rem;
  }

  .article-content {
    padding: 2.5rem 3rem;
  }
}