:root {
    --primary-color: #2563eb;
    --primary-dark: #1e40af;
    --secondary-color: #10b981;
    --accent-color: #f59e0b;
    --font-color: #1f2937;
    --font-light: #6b7280;
    --background-color: #f9fafb;
    --surface-color: #ffffff;
    --border-color: #e5e7eb;
    --shadow-sm: 0 1px 3px rgba(0,0,0,0.1);
    --shadow-md: 0 4px 6px rgba(0,0,0,0.1);
    --shadow-lg: 0 10px 25px rgba(0,0,0,0.1);
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
    color: var(--font-color);
    background: linear-gradient(135deg, var(--background-color) 0%, #f3f4f6 100%);
    line-height: 1.6;
    min-height: 100vh;
    padding: 0;
    margin: 0;
}

header.navbar {
    background: var(--surface-color);
    border-bottom: 1px solid var(--border-color);
    box-shadow: var(--shadow-md);
    position: sticky;
    top: 0;
    z-index: 100;
}

.navbar-content {
    max-width: 900px;
    margin: 0 auto;
    padding: 15px 20px;
}

main {
    padding: 0 20px;
}

.content-heading {
    font-size: 1.5em;
    font-weight: 700;
    color: var(--font-color);
    margin: 30px auto 20px;
    max-width: 900px;
    padding: 0 20px;
}

h1 {
    font-size: 2.5em;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin: 0;
    letter-spacing: -0.5px;
}

.site-tagline {
    color: var(--font-light);
    font-size: 1.1em;
    margin: 0;
    padding:5px 0 0 0
}

section {
    background: var(--surface-color);
    border-radius: 12px;
    padding: 0;
    margin: 30px auto;
    max-width: 900px;
    box-shadow: var(--shadow-md);
    overflow: hidden;
    transition: all 0.3s ease;
}

section h2 {
    font-size: 1.8em;
    color: var(--surface-color);
    margin-bottom: 0;
    font-weight: 700;
}

.section-header {
  text-align: center;
  background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
  padding: 30px 20px;
  position: relative;
  overflow: hidden;
}

.section-header::before {
  content: '';
  position: absolute;
  top: -50%;
  right: -50%;
  width: 200%;
  height: 200%;
  background: radial-gradient(circle, rgba(255,255,255,0.1) 1px, transparent 1px);
  background-size: 50px 50px;
  animation: float 20s infinite linear;
}

.section-header > * {
  position: relative;
  z-index: 1;
}

@keyframes float {
  0% { transform: translate(0, 0); }
  100% { transform: translate(50px, 50px); }
}

.section-body {
  padding: 30px 25px;
  color: var(--font-color);
}

.section-body p {
  color: var(--font-light);
  margin-bottom: 18px;
  font-size: 0.95em;
}

.section-body p:last-child {
  margin-bottom: 0;
}

#course-display video {
    width: 100%;
    border-radius: 8px;
    margin: 15px 0;
    box-shadow: var(--shadow-md);
    display: block;
}

.error-container {
    text-align: center;
    max-width: 600px;
    margin: 60px auto;
}

.error-icon {
    width: 80px;
    height: 80px;
    margin: 0 auto 30px;
    background: linear-gradient(135deg, #ef4444 0%, #dc2626 100%);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 2.5em;
    color: var(--surface-color);
    font-weight: bold;
    box-shadow: 0 20px 40px rgba(239, 68, 68, 0.3);
    animation: pulse 2s infinite;
}

@keyframes pulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); }
}

.error-indicator {
    text-align: center;
    margin: 0 !important;
}

.btn-blue {
    background: linear-gradient(135deg, var(--primary-color) 0%, var(--primary-dark) 100%);
    color: var(--surface-color);
    border: none;
    padding: 12px 28px;
    border-radius: 8px;
    cursor: pointer;
    font-size: 0.95em;
    font-weight: 600;
    transition: all 0.3s ease;
    box-shadow: 0 4px 12px rgba(37, 99, 235, 0.3);
    margin-top: 20px;
    display: inline-block;
}

.btn-blue:hover {
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(37, 99, 235, 0.4);
}

.btn-blue:active {
    transform: translateY(0);
}

.btn-blue:hover {
    background-color: var(--secondary-color);
}