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

html,
body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen, Ubuntu, Cantarell, "Open Sans", "Helvetica Neue", sans-serif;
  background-color: #f5f5f7;
  color: #1d1d1f;
  line-height: 1.6;
}

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

.container {
  width: 90%;
  max-width: 1100px;
  margin: 0 auto;
}

.site-header {
  background-color: #fff;
  border-bottom: 1px solid #d2d2d7;
  position: sticky;
  top: 0;
  z-index: 100;
}

.site-header .container {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 1rem 0;
  gap: 2rem;
}

.logo {
  font-size: 1.5rem;
  font-weight: 700;
  white-space: nowrap;
}

.nav {
  position: relative;
}

.nav-list {
  list-style: none;
  display: flex;
  align-items: center;
  gap: 0.8rem;
}

.nav-home > a,
.nav-group-toggle {
  font-weight: 600;
  padding: 0.45rem 0.7rem;
  border-radius: 8px;
  transition: color 0.2s, background-color 0.2s;
}

.nav-group-toggle {
  border: none;
  background: transparent;
  color: #1d1d1f;
  cursor: pointer;
}

.nav-home > a:hover,
.nav-group-toggle:hover,
.nav-home > a.active,
.nav-group.active-group > .nav-group-toggle {
  color: #0071e3;
  background-color: #eef5ff;
}

.nav-group {
  position: relative;
}

/* Bridge closes the hover gap between toggle and submenu on desktop */
.nav-group::after {
  content: "";
  position: absolute;
  top: 100%;
  left: 0;
  right: 0;
  height: 0.45rem;
}

.submenu {
  list-style: none;
  position: absolute;
  top: 100%;
  margin-top: 0.35rem;
  left: 0;
  min-width: 220px;
  background: #fff;
  border: 1px solid #d2d2d7;
  border-radius: 10px;
  box-shadow: 0 8px 20px rgba(0, 0, 0, 0.1);
  padding: 0.5rem;
  display: none;
}

.submenu a {
  display: block;
  padding: 0.55rem 0.7rem;
  border-radius: 6px;
  font-weight: 500;
}

.submenu a:hover,
.submenu a.active {
  background-color: #eef5ff;
  color: #0071e3;
}

.nav-group:hover .submenu,
.nav-group:focus-within .submenu,
.nav-group.open .submenu {
  display: block;
}

.burger {
  display: none;
  flex-direction: column;
  gap: 4px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 0.5rem;
}

.burger span {
  display: block;
  width: 25px;
  height: 3px;
  background-color: #1d1d1f;
  border-radius: 2px;
}

.hero {
  background-color: #fff;
  padding: 4rem 0;
  text-align: center;
}

.hero h1 {
  font-size: 2.5rem;
  margin-bottom: 1rem;
}

.hero p {
  font-size: 1.1rem;
  margin-bottom: 2rem;
  color: #5e5e61;
}

.topic-grid {
  margin-top: 2.5rem;
  display: grid;
  gap: 2rem;
  text-align: left;
}

.topic-group h2 {
  margin-bottom: 1rem;
  font-size: 1.35rem;
}

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1rem;
}

.card {
  background-color: #f5f5f7;
  border-radius: 12px;
  padding: 1.2rem;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.08);
  transition: transform 0.2s, box-shadow 0.2s;
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 6px 14px rgba(0, 0, 0, 0.13);
}

.card h3,
.card h2 {
  font-size: 1.1rem;
  margin-bottom: 0.4rem;
}

.card p {
  color: #5e5e61;
  font-size: 0.95rem;
}

.content {
  padding: 3rem 0;
  background-color: #fff;
}

.content h1 {
  font-size: 2rem;
  margin-bottom: 1.5rem;
}

.post {
  margin-bottom: 2rem;
}

.post h2 {
  font-size: 1.5rem;
  margin-bottom: 0.5rem;
}

.post p,
.post li {
  color: #3c3c3f;
}

.post pre {
  background-color: #f2f2f2;
  padding: 1rem;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1rem 0;
}

.post code {
  font-family: "Courier New", Courier, monospace;
  font-size: 0.95rem;
}

.quick-links {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 1rem;
  margin-bottom: 2rem;
}

.site-footer {
  background-color: #fff;
  border-top: 1px solid #d2d2d7;
  padding: 1.5rem 0;
  text-align: center;
}

.site-footer p {
  color: #6e6e73;
  font-size: 0.9rem;
}

@media (max-width: 768px) {
  .site-header .container {
    align-items: flex-start;
  }

  .nav-list {
    position: absolute;
    top: 100%;
    right: 0;
    flex-direction: column;
    align-items: stretch;
    background-color: #fff;
    width: min(90vw, 280px);
    border: 1px solid #d2d2d7;
    border-radius: 8px;
    overflow: hidden;
    max-height: 0;
    transition: max-height 0.3s ease;
    gap: 0;
  }

  .nav-list.open {
    max-height: 85vh;
    overflow-y: auto;
  }

  .nav-home > a,
  .nav-group-toggle,
  .submenu a {
    width: 100%;
    text-align: left;
    border-radius: 0;
    padding: 0.9rem 1rem;
  }

  .nav-group {
    border-top: 1px solid #d2d2d7;
  }

  .nav-group::after {
    display: none;
  }

  .submenu {
    position: static;
    min-width: 0;
    border: none;
    border-top: 1px solid #d2d2d7;
    border-radius: 0;
    box-shadow: none;
    padding: 0;
    display: none;
  }

  .nav-group.open .submenu,
  .nav-group.active-group .submenu {
    display: block;
  }

  .burger {
    display: flex;
  }
}