/* ===== CSS Variables ===== */
:root {
  /* Colors */
  --color-bg: #ffffff;
  --color-bg-subtle: #f5f5f5;
  --color-text: #1a1a1a;
  --color-text-muted: #666666;
  --color-border: #e0e0e0;
  --color-accent: #222222;
  --color-accent-hover: #444444;

  /* Typography */
  --font-sans: 'Noto Sans TC', 'Helvetica Neue', Arial, sans-serif;
  --font-size-base: 16px;
  --line-height-base: 1.6;

  /* Spacing */
  --space-xs: 0.25rem;
  --space-sm: 0.5rem;
  --space-md: 1rem;
  --space-lg: 1.5rem;
  --space-xl: 2rem;
  --space-2xl: 3rem;
  --space-3xl: 4rem;

  /* Layout */
  --container-max: 1200px;
  --nav-height: 64px;

  /* Breakpoints (reference only — use in media queries) */
  /* --bp-tablet: 768px  */
  /* --bp-desktop: 1024px */

  /* Transitions */
  --transition: 0.2s ease;
}

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

html {
  font-size: var(--font-size-base);
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-sans);
  background-color: var(--color-bg);
  color: var(--color-text);
  line-height: var(--line-height-base);
  -webkit-font-smoothing: antialiased;
}

img, svg {
  display: block;
  max-width: 100%;
}

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

ul, ol {
  list-style: none;
}

button {
  background: none;
  border: none;
  cursor: pointer;
  font: inherit;
}

/* ===== Layout Utilities ===== */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-md);
}

/* ===== Navbar ===== */
.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  background-color: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  height: var(--nav-height);
}

.navbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-md);
}

.nav-logo {
  display: flex;
  align-items: center;
  gap: var(--space-sm);
  font-weight: 700;
  font-size: 1.1rem;
}

.logo-img {
  height: 33px;
  width: auto;
}

.nav-links {
  display: none;
  flex-direction: column;
  position: absolute;
  top: var(--nav-height);
  left: 0;
  right: 0;
  background-color: var(--color-bg);
  border-bottom: 1px solid var(--color-border);
  padding: var(--space-md);
  gap: var(--space-sm);
}

.nav-links.is-open {
  display: flex;
}

.nav-links a {
  display: block;
  padding: var(--space-sm) var(--space-md);
  border-radius: 4px;
  transition: background-color var(--transition);
}

.nav-links a:hover {
  background-color: var(--color-bg-subtle);
}

/* Hamburger */
.hamburger {
  display: flex;
  flex-direction: column;
  justify-content: center;
  gap: 5px;
  width: 32px;
  height: 32px;
  padding: 4px;
}

.hamburger-line {
  display: block;
  height: 2px;
  background-color: var(--color-text);
  transition: transform var(--transition), opacity var(--transition);
}

.hamburger.is-active .hamburger-line:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}
.hamburger.is-active .hamburger-line:nth-child(2) {
  opacity: 0;
}
.hamburger.is-active .hamburger-line:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ===== Main Content Offset ===== */
main {
  padding-top: var(--nav-height);
  min-height: calc(100vh - var(--nav-height));
}

/* ===== Footer ===== */
.site-footer {
  background-color: var(--color-bg-subtle);
  border-top: 1px solid var(--color-border);
  padding: var(--space-2xl) var(--space-md);
}

.footer-inner {
  max-width: var(--container-max);
  margin-inline: auto;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-lg);
  text-align: center;
}

.footer-brand {
  font-weight: 700;
  font-size: 1.1rem;
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-md);
}

.footer-links a {
  font-size: 0.9rem;
  color: var(--color-text-muted);
  transition: color var(--transition);
}

.footer-links a:hover {
  color: var(--color-text);
}

.footer-social {
  display: flex;
  gap: var(--space-md);
}

.footer-social a {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 36px;
  height: 36px;
  transition: opacity var(--transition);
}

.footer-social a:hover {
  opacity: 0.7;
}

.footer-social img {
  width: 24px;
  height: 24px;
}

.footer-copy {
  font-size: 0.85rem;
  color: var(--color-text-muted);
}

/* ===== Tablet (768px+) ===== */
@media (min-width: 768px) {
  .container {
    padding-inline: var(--space-xl);
  }

  .nav-links {
    display: flex;
    flex-direction: row;
    position: static;
    border: none;
    padding: 0;
    gap: var(--space-xs);
  }

  .hamburger {
    display: none;
  }
}

/* ===== Desktop (1024px+) ===== */
@media (min-width: 1024px) {
  .container {
    padding-inline: var(--space-2xl);
  }

  .nav-links {
    gap: var(--space-sm);
  }
}