:root {
  --primary: #7c3aed;
  --secondary: #06b6d4;

  --bg-dark: #050814;
  --text-dark: #e2e8f0;

  --bg-light: #f8fafc;
  --text-light: #0f172a;

  --glass-bg-dark: rgba(255, 255, 255, 0.06);
  --glass-border-dark: rgba(255, 255, 255, 0.12);

  --glass-bg-light: rgba(255, 255, 255, 0.65);
  --glass-border-light: rgba(15, 23, 42, 0.12);

  --shadow-dark: 0 12px 35px rgba(0, 0, 0, 0.35);
  --shadow-light: 0 12px 35px rgba(15, 23, 42, 0.12);
}

/* Default Dark */
body {
  font-family: "Poppins", sans-serif;
  background: radial-gradient(circle at top, rgba(124, 58, 237, 0.18), transparent 60%),
              radial-gradient(circle at bottom, rgba(6, 182, 212, 0.12), transparent 60%),
              var(--bg-dark);
  color: var(--text-dark);
  transition: 0.25s ease;
}

/* Light Mode */
body.light-mode {
  background: radial-gradient(circle at top, rgba(37, 99, 235, 0.18), transparent 60%),
              radial-gradient(circle at bottom, rgba(124, 58, 237, 0.12), transparent 60%),
              var(--bg-light);
  color: var(--text-light);
}

/* Navbar */
.glass-navbar {
  background: var(--glass-bg-dark);
  border-bottom: 1px solid var(--glass-border-dark);
  backdrop-filter: blur(14px);
}

body.light-mode .glass-navbar {
  background: var(--glass-bg-light);
  border-bottom: 1px solid var(--glass-border-light);
}

.navbar-brand {
  font-size: 1.5rem;
}

.brand-text {
  color: var(--text-dark);
}

.brand-id {
  color: var(--primary);
  text-shadow: 0 0 18px rgba(124, 58, 237, 0.5);
}

body.light-mode .brand-text {
  color: var(--text-light);
}

.nav-link {
  font-weight: 800;
  color: var(--text-dark);
  opacity: 0.8;
  transition: 0.2s ease;
}

.nav-link:hover {
  opacity: 1;
  color: var(--primary);
}

body.light-mode .nav-link {
  color: var(--text-light);
}

/* Buttons */
.btn-glass {
  background: var(--glass-bg-dark);
  border: 1px solid var(--glass-border-dark);
  color: var(--text-dark);
  border-radius: 14px;
  padding: 10px 14px;
  font-weight: 800;
  transition: 0.2s ease;
}

.btn-glass:hover {
  transform: translateY(-2px);
  border-color: var(--primary);
  box-shadow: 0 0 18px rgba(124, 58, 237, 0.3);
}

body.light-mode .btn-glass {
  background: var(--glass-bg-light);
  border: 1px solid var(--glass-border-light);
  color: var(--text-light);
}

.btn-primary-custom {
  background: linear-gradient(135deg, var(--primary), var(--secondary));
  border: none;
  padding: 12px 18px;
  border-radius: 16px;
  font-weight: 900;
  color: white;
  transition: 0.2s ease;
}

.btn-primary-custom:hover {
  transform: translateY(-3px);
  box-shadow: 0 0 22px rgba(124, 58, 237, 0.4);
  color: white;
}

/* Header */
.lesson-header {
  padding: 60px 0 30px;
}

.lesson-glass {
  background: var(--glass-bg-dark);
  border: 1px solid var(--glass-border-dark);
  border-radius: 22px;
  backdrop-filter: blur(14px);
  box-shadow: var(--shadow-dark);
}

body.light-mode .lesson-glass {
  background: var(--glass-bg-light);
  border: 1px solid var(--glass-border-light);
  box-shadow: var(--shadow-light);
}

.lesson-badge {
  display: inline-block;
  padding: 7px 16px;
  border-radius: 999px;
  font-weight: 900;
  font-size: 0.85rem;
  background: rgba(124, 58, 237, 0.16);
  border: 1px solid var(--glass-border-dark);
  color: var(--primary);
}

.lesson-title {
  font-size: 2.3rem;
  font-weight: 900;
  text-shadow: 0 0 18px rgba(124, 58, 237, 0.35);
}

.lesson-desc {
  opacity: 0.85;
  line-height: 1.7;
  max-width: 750px;
}

.lesson-meta .meta-box {
  background: rgba(0, 0, 0, 0.18);
  border: 1px solid var(--glass-border-dark);
  padding: 10px 14px;
  border-radius: 14px;
  display: flex;
  align-items: center;
  gap: 10px;
  font-weight: 750;
}

body.light-mode .lesson-meta .meta-box {
  background: rgba(255, 255, 255, 0.65);
  border: 1px solid var(--glass-border-light);
}

/* Content */
.lesson-content {
  padding: 40px 0 90px;
}

.lesson-section {
  background: var(--glass-bg-dark);
  border: 1px solid var(--glass-border-dark);
  border-radius: 18px;
  padding: 25px;
  margin-bottom: 18px;
  backdrop-filter: blur(14px);
  transition: 0.25s ease;
  box-shadow: var(--shadow-dark);
}

.lesson-section:hover {
  transform: translateY(-4px);
  border-color: var(--primary);
  box-shadow: 0 0 25px rgba(124, 58, 237, 0.18);
}

body.light-mode .lesson-section {
  background: var(--glass-bg-light);
  border: 1px solid var(--glass-border-light);
  box-shadow: var(--shadow-light);
}

.lesson-section h3 {
  font-weight: 900;
  margin-bottom: 12px;
}

.lesson-section p {
  opacity: 0.88;
  line-height: 1.7;
}

.lesson-list {
  padding-left: 18px;
  opacity: 0.9;
}

.lesson-list li {
  margin-bottom: 8px;
}

/* TOC */
.toc-glass {
  background: var(--glass-bg-dark);
  border: 1px solid var(--glass-border-dark);
  border-radius: 18px;
  backdrop-filter: blur(14px);
  box-shadow: var(--shadow-dark);
}

body.light-mode .toc-glass {
  background: var(--glass-bg-light);
  border: 1px solid var(--glass-border-light);
  box-shadow: var(--shadow-light);
}

.toc-list {
  list-style: none;
  padding: 0;
  margin: 0;
}

.toc-list li {
  margin-bottom: 10px;
}

.toc-list a {
  text-decoration: none;
  font-weight: 850;
  color: var(--text-dark);
  opacity: 0.75;
  transition: 0.2s ease;
}

.toc-list a:hover {
  opacity: 1;
  color: var(--primary);
}

body.light-mode .toc-list a {
  color: var(--text-light);
}

.toc-line {
  border-color: var(--glass-border-dark);
}

body.light-mode .toc-line {
  border-color: var(--glass-border-light);
}

/* Code */
.code-box {
  background: rgba(0, 0, 0, 0.35);
  border: 1px solid var(--glass-border-dark);
  border-radius: 16px;
  padding: 16px;
  overflow-x: auto;
  margin-top: 14px;
}

body.light-mode .code-box {
  background: rgba(255, 255, 255, 0.8);
  border: 1px solid var(--glass-border-light);
}

.code-box pre {
  margin: 0;
}

.code-box code {
  color: var(--text-dark);
  font-weight: 600;
  font-size: 0.9rem;
}

body.light-mode .code-box code {
  color: var(--text-light);
}

/* Info */
.info-box {
  display: flex;
  gap: 12px;
  align-items: center;
  padding: 14px 16px;
  border-radius: 16px;
  margin-top: 18px;
  border: 1px solid var(--glass-border-dark);
  background: rgba(124, 58, 237, 0.14);
}

body.light-mode .info-box {
  border: 1px solid var(--glass-border-light);
}

.info-box i {
  font-size: 1.2rem;
  color: var(--primary);
}

/* Video Card */
.video-card {
  background: var(--glass-bg-dark);
  border: 1px solid var(--glass-border-dark);
  border-radius: 18px;
  padding: 20px;
  backdrop-filter: blur(14px);
  box-shadow: var(--shadow-dark);
  margin-bottom: 30px;
}

body.light-mode .video-card {
  background: var(--glass-bg-light);
  border: 1px solid var(--glass-border-light);
  box-shadow: var(--shadow-light);
}

.video-wrapper {
  position: relative;
  width: 100%;
  padding-top: 56.25%;
  border-radius: 16px;
  overflow: hidden;
  border: 1px solid var(--glass-border-dark);
}

body.light-mode .video-wrapper {
  border: 1px solid var(--glass-border-light);
}

.video-wrapper iframe {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

.video-desc {
  opacity: 0.85;
  line-height: 1.7;
}

/* Table */
.glass-table {
  border-radius: 16px;
  overflow: hidden;
  border: 1px solid var(--glass-border-dark);
  margin-top: 15px;
  background: rgba(0, 0, 0, 0.22);
}

body.light-mode .glass-table {
  border: 1px solid var(--glass-border-light);
  background: rgba(255, 255, 255, 0.7);
}

.custom-table {
  margin: 0;
  color: var(--text-dark) !important;
}

.custom-table thead {
  background: rgba(124, 58, 237, 0.18);
}

.custom-table th {
  color: var(--primary) !important;
  font-weight: 900;
  border-bottom: 1px solid var(--glass-border-dark) !important;
}

.custom-table td {
  color: var(--text-dark) !important;
  font-weight: 600;
  opacity: 0.9;
  border-bottom: 1px solid rgba(255, 255, 255, 0.06) !important;
}

.custom-table tr:last-child td {
  border-bottom: none !important;
}

body.light-mode .custom-table {
  color: var(--text-light) !important;
}

body.light-mode .custom-table td {
  color: var(--text-light) !important;
  border-bottom: 1px solid rgba(15, 23, 42, 0.08) !important;
}

body.light-mode .custom-table th {
  border-bottom: 1px solid rgba(15, 23, 42, 0.12) !important;
}

/* Challenge */
.challenge-box {
  padding: 18px;
  border-radius: 18px;
  border: 1px solid var(--glass-border-dark);
  background: rgba(34, 197, 94, 0.14);
  margin-top: 14px;
}

body.light-mode .challenge-box {
  border: 1px solid var(--glass-border-light);
}

/* Footer */
.footer-section {
  padding: 35px 0;
  border-top: 1px solid var(--glass-border-dark);
  background: rgba(0, 0, 0, 0.15);
}

body.light-mode .footer-section {
  border-top: 1px solid var(--glass-border-light);
  background: rgba(255, 255, 255, 0.6);
}

.dev-link {
  color: var(--primary);
  font-weight: 900;
  text-decoration: none;
}

.dev-link:hover {
  text-decoration: underline;
}