:root {
    --bg-dark: #0a0e14;
    --card-dark: #121821;
    --accent: #007aff; /* Apple Blue accent */
    --text-white: #ffffff;
    --text-muted: #8e8e93;
    --glass: rgba(255, 255, 255, 0.05);
}

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
    background-color: var(--bg-dark);
    color: var(--text-white);
    margin: 0;
    -webkit-font-smoothing: antialiased;
}

/* Header & Glassmorphism */
.header {
    background: rgba(10, 14, 20, 0.8);
    backdrop-filter: blur(15px);
    border-bottom: 1px solid var(--glass);
    z-index: 1000;
}

.logo { font-weight: 800; font-size: 1.5rem; letter-spacing: -1px; }
.logo span { color: var(--accent); }

/* Buttons */
.btn-primary { background-color: var(--accent); border: none; border-radius: 12px; padding: 12px 24px; font-weight: 600; transition: all 0.3s; }
.btn-primary:hover { transform: translateY(-2px); box-shadow: 0 4px 15px rgba(0, 122, 255, 0.4); }

/* Cards */
.chapter-card {
    background: var(--card-dark);
    border: 1px solid var(--glass);
    border-radius: 16px;
    overflow: hidden;
    cursor: pointer;
    transition: transform 0.4s cubic-bezier(0.175, 0.885, 0.32, 1.275);
}
.chapter-card:hover { transform: scale(1.03); }
.card-img-wrapper { height: 160px; overflow: hidden; }
.card-img-top { width: 100%; height: 100%; object-fit: cover; opacity: 0.8; }

/* Progress */
.progress-card { background: var(--glass); padding: 15px; border-radius: 12px; }
.progress-bar { background-color: var(--accent); }

/* Audio Player UI */
.audio-player-ui { background: var(--card-dark); border: 1px solid var(--glass); }
.play-main-btn {
    background: var(--text-white);
    color: var(--bg-dark);
    width: 60px;
    height: 60px;
    border-radius: 50%;
    border: none;
    font-size: 1.5rem;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: transform 0.2s;
}
.play-main-btn:active { transform: scale(0.9); }

.speed-select {
    background: transparent;
    color: var(--text-white);
    border: 1px solid var(--glass);
    border-radius: 8px;
    padding: 5px;
}

/* Sticky Player Bottom */
.sticky-player {
    position: fixed;
    bottom: 0;
    left: 0;
    width: 100%;
    background: rgba(18, 24, 33, 0.95);
    backdrop-filter: blur(10px);
    padding: 10px 0;
    border-top: 1px solid var(--glass);
    z-index: 1001;
    animation: slideUp 0.5s forwards;
}

@keyframes slideUp { from { transform: translateY(100%); } to { transform: translateY(0); } }

/* Mobile Optimizations */
@media (max-width: 768px) {
    .display-4 { font-size: 1.8rem; }
    .hero-section { padding: 40px 20px; text-align: center; }
}