:root {
  /* Light mode */
  --text: #1f3b63;
  --card: #ffffff;
  --stroke: #e6e9ef;
  --btn1: #3b82f6;
  /* blue-500 */
  --btn2: #2563eb;
  /* blue-600 */
  --bg-gradient: linear-gradient(180deg, #ECF3FF 0%, #FFFFFF 100%);
  --slider-btn-color: #000000; /* đen */
  --train-link: #252525;
  --intro-bg-start: #e0f2fe;
  --intro-bg-end: #f0f9ff;
}

body.dark {
  /* Dark mode overrides */
  --text: #e5e7eb;
  /* text-gray-200 */
  --card: #1f2937;
  /* gray-800 */
  --stroke: #374151;
  /* gray-700 */
  --btn1: #2563eb;
  /* blue-600 */
  --btn2: #1d4ed8;
  /* blue-700 */
  --bg-gradient: linear-gradient(180deg, #111827 0%, #1f2937 100%);
  --slider-btn-color: #ffffff; /* trắng */
  --train-link: #e5e7eb;
  --intro-bg-start: #0f172a;
  --intro-bg-end: #1e293b;
}

* {
  box-sizing: border-box
}

body {
  font-family: Arial, sans-serif;
  line-height: 1.6;
  background: var(--bg-gradient);
  margin: 0;
  padding: 0;
  color: var(--text);
}

.container {
  max-width: 900px;
  margin: 0 auto;
  padding: 20px;
  background: var(--card);;
}

/* Giới thiệu */
header.intro {
  text-align: center;
  margin-bottom: 40px;
  padding: 20px;
  background: linear-gradient(135deg, var(--intro-bg-start), var(--intro-bg-end));
  border-radius: 12px;
  box-shadow: 0 2px 10px rgba(0,0,0,0.05);
}

header.intro h1 {
  font-size: 28px;
  margin-bottom: 15px;
  color: var(--text);
}

header.intro p {
  font-size: 16px;
  margin-bottom: 25px;
  max-width: 700px;
  margin-left: auto;
  margin-right: auto;
}

/* Nút quay về trang chủ */
.back-home {
  position: fixed;
  top: 20px;
  left: 20px;
  display: flex;
  align-items: center;
  gap: 6px;
  background: var(--btn-bg, #f3f4f6);
  color: var(--btn-text, #111827);
  padding: 8px 14px;
  border-radius: 8px;
  font-size: 14px;
  font-weight: 500;
  text-decoration: none;
  box-shadow: 0 2px 6px rgba(0,0,0,0.15);
  transition: all 0.2s ease-in-out;
  z-index: 1000;
}

.back-home:hover {
  background: var(--btn-hover-bg, #e5e7eb);
  transform: translateX(-3px);
}

.back-home .icon {
  width: 18px;
  height: 18px;
}

/* Dark mode */
body.dark .back-home {
  background: var(--btn-bg-dark, #1f2937);
  color: var(--btn-text-dark, #f9fafb);
  box-shadow: 0 2px 6px rgba(0,0,0,0.6);
}

body.dark .back-home:hover {
  background: var(--btn-hover-bg-dark, #374151);
}

/* About Project */
.about-project {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 15px 30px;
  justify-items: start;
  max-width: 700px;
  margin: 0 auto;
  text-align: left;
}

.about-item {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  font-size: 15px;
}

.about-item .icon {
  font-size: 24px;
  flex-shrink: 0;
}

.about-item p {
  margin: 5px 0 0;
}

/* Mobile */
@media (max-width: 600px) {
  .about-project {
    grid-template-columns: 1fr;
  }
}


.guide h2 {
  font-size: 22px;
  margin-bottom: 20px;
  border-bottom: 2px solid #ddd;
  padding-bottom: 5px;
}

.step {
  margin-bottom: 40px;
}

.step h3 {
  font-size: 18px;
  margin-bottom: 10px;
  color: #1d4ed8;
}

.step img {
  display: block;
  margin: 15px auto;
  max-width: 100%;
  border-radius: 6px;
  box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.qr-section {
  display: flex;
  justify-content: center;
  gap: 40px;
  flex-wrap: wrap;
  margin-top: 40px;
  padding: 20px 0;
  border-top: 2px solid #eee;
}

.qr-card {
  text-align: center;
}

.qr-card img {
  width: 180px;
  height: 180px;
  object-fit: cover;
  border-radius: 8px;
  border: 1px solid #ddd;
}

.qr-card p {
  margin-top: 10px;
  font-weight: bold;
}

.theme-toggle {
  position: fixed;
  top: 30px;
  right: 30px;
  width: 44px;
  height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: 9999px;
  background: var(--btn-bg);
  color: var(--text);
  border: 1px solid var(--border);
  box-shadow: var(--shadow);
  cursor: pointer;
  transition: transform 160ms ease, box-shadow 160ms ease, background-color 160ms ease, border-color 160ms ease;
  z-index: 30
}

.theme-toggle:hover {
  transform: translateY(-1px);
  box-shadow: var(--shadow-hover)
}

.theme-toggle:focus-visible {
  outline: 3px solid color-mix(in oklab, var(--focus), white 20%);
  outline-offset: 3px
}

.theme-toggle .icon {
  font-size: 18px;
  line-height: 1;
  display: inline-block;
  transform-origin: 50% 50%
}

.theme-toggle.spin .icon {
  animation: toggle-spin 480ms ease-in-out
}

@keyframes toggle-spin {
  from {
    transform: rotate(0) scale(1)
  }

  50% {
    transform: rotate(140deg) scale(1.05)
  }

  to {
    transform: rotate(180deg) scale(1)
  }
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0
}