:root {
  /* Light Theme */
  --bg-color: #f8f9fa;
  --text-color: #212529;
  --card-bg: rgba(255, 255, 255, 0.8);
  --accent-color: #6366f1;
  --nav-bg: rgba(255, 255, 255, 0.7);
  --border-color: #e9ecef;
  --transition: all 0.3s ease;
}

[data-theme="dark"] {
  /* Dark Theme */
  --bg-color: #0f172a;
  --text-color: #f1f5f9;
  --card-bg: rgba(30, 41, 59, 0.8);
  --accent-color: #818cf8;
  --nav-bg: rgba(15, 23, 42, 0.7);
  --border-color: #334155;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Pretendard', -apple-system, BlinkMacSystemFont, system-ui, Roboto, sans-serif;
}

body {
  background-color: var(--bg-color);
  color: var(--text-color);
  transition: var(--transition);
  line-height: 1.6;
}

/* Glassmorphism Navigation */
nav {
  position: sticky;
  top: 0;
  background: var(--nav-bg);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--border-color);
  z-index: 1000;
  padding: 1rem 5%;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.logo {
  font-size: 1.5rem;
  font-weight: 800;
  color: var(--accent-color);
  text-decoration: none;
}

.nav-actions {
  display: flex;
  gap: 1.5rem;
  align-items: center;
}

#theme-toggle {
  background: none;
  border: none;
  cursor: pointer;
  font-size: 1.2rem;
  color: var(--text-color);
}

/* Main Layout */
main {
  max-width: 1000px;
  margin: 2rem auto;
  padding: 0 1rem;
}

.hero {
  text-align: center;
  padding: 4rem 0;
  animation: fadeInDown 0.8s ease;
}

.hero h1 {
  font-size: 3rem;
  margin-bottom: 1rem;
}

/* Search & Filter Section */
.controls {
  margin-bottom: 3rem;
  display: flex;
  flex-direction: column;
  gap: 1rem;
  align-items: center;
}

#search-input {
  width: 100%;
  max-width: 500px;
  padding: 0.8rem 1.5rem;
  border-radius: 50px;
  border: 1px solid var(--border-color);
  background: var(--card-bg);
  color: var(--text-color);
  font-size: 1rem;
  outline: none;
  transition: var(--transition);
}

#search-input:focus {
  border-color: var(--accent-color);
  box-shadow: 0 0 10px rgba(99, 102, 241, 0.3);
}

.tags-filter {
  display: flex;
  gap: 0.5rem;
  flex-wrap: wrap;
  justify-content: center;
}

.tag-btn {
  padding: 0.4rem 1rem;
  border-radius: 20px;
  background: var(--card-bg);
  border: 1px solid var(--border-color);
  cursor: pointer;
  color: var(--text-color);
  transition: var(--transition);
}

.tag-btn:hover, .tag-btn.active {
  background: var(--accent-color);
  color: white;
  border-color: var(--accent-color);
}

/* Post Card Grid */
.post-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
  gap: 2rem;
}

.post-card {
  background: var(--card-bg);
  border: 1px solid var(--border-color);
  border-radius: 15px;
  padding: 1.5rem;
  transition: var(--transition);
  cursor: pointer;
  display: flex;
  flex-direction: column;
  position: relative;
  overflow: hidden;
  backdrop-filter: blur(5px);
}

.post-card:hover {
  transform: translateY(-10px);
  box-shadow: 0 10px 30px rgba(0,0,0,0.1);
}

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

.post-card .date {
  font-size: 0.85rem;
  color: #888;
  margin-bottom: 0.5rem;
}

.post-card .summary {
  font-size: 0.95rem;
  margin-bottom: 1.5rem;
}

.post-card .tags {
  display: flex;
  gap: 0.4rem;
  margin-top: auto;
}

.tag-small {
  font-size: 0.75rem;
  padding: 0.2rem 0.6rem;
  background: rgba(99, 102, 241, 0.1);
  color: var(--accent-color);
  border-radius: 5px;
}

/* Post Detail */
.post-detail {
  background: var(--card-bg);
  padding: 3rem;
  border-radius: 20px;
  border: 1px solid var(--border-color);
  animation: fadeInUp 0.5s ease;
}

.post-detail header {
  margin-bottom: 2rem;
  text-align: center;
}

.post-content img {
  max-width: 100%;
  border-radius: 10px;
}

/* Animations */
@keyframes fadeInDown {
  from { opacity: 0; transform: translateY(-30px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeInUp {
  from { opacity: 0; transform: translateY(30px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Footer */
footer {
  text-align: center;
  padding: 4rem 0;
  border-top: 1px solid var(--border-color);
  margin-top: 4rem;
  font-size: 0.9rem;
  color: #888;
}

@media (max-width: 600px) {
  .hero h1 { font-size: 2rem; }
  .post-detail { padding: 1.5rem; }
}