:root {
  --bg: #ffffff;
  --text: #333333;
  --card-bg: #f9f9f9;
  --accent: #4a6cf7;
  --border: #e0e0e0;
  --shadow: rgba(0,0,0,0.08);
}
[data-theme="dark"] {
  --bg: #121212;
  --text: #f0f0f0;
  --card-bg: #1e1e1e;
  --border: #333333;
  --shadow: rgba(0,0,0,0.3);
}

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

body {
  font-family: "Helvetica Neue", "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  background-color: var(--bg);
  color: var(--text);
  line-height: 1.6;
  transition: background-color 0.3s, color 0.3s;
}

header {
  padding: 1.5rem 5%;
  display: flex;
  justify-content: space-between;
  align-items: center;
  border-bottom: 1px solid var(--border);
  flex-wrap: wrap;
  gap: 1rem;
}

.logo {
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--accent);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}

nav a {
  margin-left: 1.2rem;
  text-decoration: none;
  color: var(--text);
  font-weight: 500;
}

.header-right {
  display: flex;
  align-items: center;
  gap: 0.8rem;
}

.lang-switch {
  padding: 0.3rem;
  border: 1px solid var(--border);
  border-radius: 4px;
  background: var(--bg);
  color: var(--text);
}

.theme-toggle {
  background: none;
  border: none;
  font-size: 1.3rem;
  cursor: pointer;
  color: var(--text);
}

main {
  max-width: 800px;
  margin: 2rem auto;
  padding: 0 5%;
}

.hero {
  text-align: center;
  margin-bottom: 2.5rem;
}

.hero h1 {
  font-size: 2.2rem;
  margin-bottom: 0.8rem;
}

.hero p {
  font-size: 1.1rem;
  opacity: 0.9;
}

.posts h2,
.section h2 {
  margin-bottom: 1.5rem;
  color: var(--accent);
}

.post-card {
  background: var(--card-bg);
  border-radius: 12px;
  padding: 1.5rem;
  margin-bottom: 1.5rem;
  box-shadow: 0 4px 12px var(--shadow);
  border: 1px solid var(--border);
  transition: transform 0.2s;
}

.post-card:hover {
  transform: translateY(-3px);
}

.post-card h3 {
  margin: 0.5rem 0 0.8rem;
  color: var(--accent);
}

.read-more {
  margin-top: 0.8rem;
  padding: 0.4rem 0.8rem;
  background: var(--accent);
  color: white;
  border: none;
  border-radius: 4px;
  cursor: pointer;
}

.post-detail {
  margin-top: 1rem;
  padding-top: 1rem;
  border-top: 1px dashed var(--border);
}

.section {
  margin: 3rem 0;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
}

footer {
  text-align: center;
  padding: 2rem 5%;
  border-top: 1px solid var(--border);
  font-size: 0.9rem;
  opacity: 0.8;
}

.social-links {
  margin-bottom: 0.8rem;
}
.social-links a {
  margin: 0 0.6rem;
  font-size: 1.2rem;
  text-decoration: none;
  color: var(--text);
}

.back-to-top {
  position: fixed;
  bottom: 20px;
  right: 20px;
  background: var(--accent);
  color: white;
  border: none;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  cursor: pointer;
  display: none;
  font-size: 1.2rem;
  box-shadow: 0 2px 8px var(--shadow);
  z-index: 100;
}

.back-to-top.show {
  display: block;
}

@media (max-width: 600px) {
  header {
    flex-direction: column;
    text-align: center;
  }
  nav a {
    margin: 0 0.7rem;
  }
  .hero h1 {
    font-size: 1.8rem;
  }
}