/* ===== CSS Variables ===== */
:root {
  --bg: #f0f4f8;
  --surface: #ffffff;
  --nav-bg: #1a1a2e;
  --text-primary: #1a1a2e;
  --text-secondary: #4a5568;
  --accent: #4361ee;
  --accent-light: #4cc9f0;
  --border: #dde3ea;
  --shadow: rgba(0, 0, 0, 0.08);
  --shadow-hover: rgba(67, 97, 238, 0.2);
  --nav-text: #c8d0e0;
  --nav-link-hover: #ffffff;
  --tag-html: #4361ee;
  --tag-css: #7b2d8b;
  --tag-boxmodel: #1a7f4b;
  --page-nav-bg: rgba(26, 26, 46, 0.05);
  --btn-nav-text: #2d3748;
  --btn-nav-border: #b0bac8;
  --btn-nav-hover-bg: rgba(67, 97, 238, 0.08);
  --btn-nav-hover-text: var(--accent);
  --btn-nav-hover-border: var(--accent);
}

/* ===== Hidden Inputs (CSS-only interactivity) ===== */
.hidden-input {
  position: absolute;
  width: 0;
  height: 0;
  opacity: 0;
  pointer-events: none;
}

/* ===== Dark Mode via :checked ===== */
#dark-mode:checked ~ .site-wrapper {
  --bg: #0d1117;
  --surface: #161b22;
  --text-primary: #e6edf3;
  --text-secondary: #8b949e;
  --border: #30363d;
  --shadow: rgba(0, 0, 0, 0.3);
  --shadow-hover: rgba(67, 97, 238, 0.35);
  --page-nav-bg: rgba(0, 0, 0, 0.25);
  --btn-nav-text: rgba(255, 255, 255, 0.88);
  --btn-nav-border: rgba(255, 255, 255, 0.28);
  --btn-nav-hover-bg: rgba(255, 255, 255, 0.1);
  --btn-nav-hover-text: #ffffff;
  --btn-nav-hover-border: rgba(255, 255, 255, 0.55);
}

#dark-mode:checked ~ .site-wrapper .night-toggle {
  background: rgba(67, 97, 238, 0.25);
  color: #ffffff;
  border-color: rgba(67, 97, 238, 0.5);
}

/* ===== Reset & Base ===== */
*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Apple SD Gothic Neo',
               'Noto Sans KR', sans-serif;
  min-height: 100vh;
}

a {
  text-decoration: none;
  color: inherit;
}

/* ===== Site Wrapper ===== */
.site-wrapper {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  background: var(--bg);
  color: var(--text-primary);
  transition: background 0.3s ease, color 0.3s ease;
}

/* ===== Header ===== */
.site-header {
  background: var(--nav-bg);
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.3);
}

.nav {
  display: flex;
  align-items: center;
  gap: 1.5rem;
  padding: 0 2rem;
  height: 60px;
}

.brand {
  font-size: 1rem;
  font-weight: 700;
  color: #ffffff;
  letter-spacing: -0.02em;
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  text-decoration: none;
}

.brand-icon {
  font-size: 1.3rem;
  color: var(--accent);
}

.nav-spacer {
  flex: 1;
}

/* ===== Breadcrumb (inner pages) ===== */
.nav-breadcrumb {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  flex: 1;
  font-size: 0.82rem;
  color: var(--nav-text);
}

.nav-breadcrumb a {
  color: var(--nav-text);
  transition: color 0.2s;
}

.nav-breadcrumb a:hover {
  color: #ffffff;
}

.nav-breadcrumb .sep {
  opacity: 0.4;
}

.nav-breadcrumb .current {
  color: rgba(255, 255, 255, 0.8);
  font-weight: 500;
}

/* ===== Night Mode Toggle ===== */
.night-toggle {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  padding: 0.3rem 0.9rem;
  border-radius: 20px;
  border: 1.5px solid rgba(255, 255, 255, 0.2);
  color: var(--nav-text);
  font-size: 0.82rem;
  font-weight: 500;
  cursor: pointer;
  transition: background 0.2s, color 0.2s, border-color 0.2s;
  user-select: none;
  white-space: nowrap;
}

.night-toggle:hover {
  background: rgba(255, 255, 255, 0.1);
  color: #ffffff;
}

/* ===== Footer ===== */
.site-footer {
  text-align: center;
  padding: 2rem;
  font-size: 0.78rem;
  color: var(--text-secondary);
  border-top: 1px solid var(--border);
  margin-top: auto;
}

/* ===== Page Navigation (prev/next/quiz) ===== */
.page-nav {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  align-items: center;
  padding: 0.5rem 2rem;
  background: var(--page-nav-bg);
  border-bottom: 1px solid var(--border);
}

.page-nav > div:nth-child(1) { text-align: left; }
.page-nav > div:nth-child(2) { text-align: center; }
.page-nav > div:nth-child(3) { text-align: right; }

.btn-nav {
  display: inline-flex;
  align-items: center;
  padding: 0.4rem 1.05rem;
  border-radius: 20px;
  border: 1.5px solid var(--btn-nav-border);
  color: var(--btn-nav-text);
  font-size: 0.83rem;
  font-weight: 600;
  text-decoration: none;
  transition: background 0.2s, color 0.2s, border-color 0.2s;
  white-space: nowrap;
}

.btn-nav:hover {
  background: var(--btn-nav-hover-bg);
  color: var(--btn-nav-hover-text);
  border-color: var(--btn-nav-hover-border);
}

.btn-nav--accent {
  background: var(--accent);
  color: #ffffff;
  border-color: var(--accent);
}

.btn-nav--accent:hover {
  filter: brightness(1.12);
}

/* ===== Responsive ===== */
@media (max-width: 640px) {
  .nav {
    padding: 0 1rem;
    gap: 0.75rem;
  }

  .page-nav {
    padding: 0.5rem 1rem;
  }
}