:root {
    --primary-color: #2563eb;
    --bg-gradient: linear-gradient(135deg, #f5f7fa 0%, #c3cfe2 100%);
    --text-color: #1e293b;
    --glass-bg: rgba(255, 255, 255, 0.7);
    --glass-border: rgba(255, 255, 255, 0.5);
    --shadow-gentle: 0 10px 30px -10px rgba(0, 0, 0, 0.1);
    --shadow-deep: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Outfit', sans-serif;
}

body {
    background: var(--bg-gradient);
    min-height: 100vh;
    color: var(--text-color);
    overflow: hidden; /* Prevent body scroll, let viewport handle it if needed */
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}

.app-container {
    width: 100%;
    height: 100vh;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    position: relative;
    backdrop-filter: blur(10px);
}

/* Header */
.app-header {
    position: absolute;
    top: 2rem;
    left: 0;
    width: 100%;
    text-align: center;
    z-index: 10;
    pointer-events: none; /* Let clicks pass through to book if overlapping */
}

.app-header h1 {
    font-weight: 600;
    font-size: 1.5rem;
    letter-spacing: -0.02em;
    color: #0f172a;
    margin-bottom: 0.25rem;
    text-shadow: 0 1px 2px rgba(255,255,255,0.8);
}

.app-header p {
    font-weight: 300;
    font-size: 0.875rem;
    color: #64748b;
}

/* Loader */
.loader-overlay {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: rgba(255, 255, 255, 0.9);
    z-index: 1000;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    transition: opacity 0.5s ease, visibility 0.5s ease;
}

.loader-overlay.hidden {
    opacity: 0;
    visibility: hidden;
}

.spinner {
    width: 40px;
    height: 40px;
    border: 3px solid rgba(37, 99, 235, 0.1);
    border-radius: 50%;
    border-top-color: var(--primary-color);
    animation: spin 1s ease-in-out infinite;
    margin-bottom: 1rem;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

/* Flipbook Viewport */
.flipbook-viewport {
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    padding: 2rem;
}

.container {
    position: relative;
    /* Max limits for specific device sizes can be added here */
}

.flipbook {
    display: none; /* Hidden until loaded */
    box-shadow: var(--shadow-deep);
    /* Transition for smooth appearance */
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.6s ease-out, transform 0.6s ease-out;
}

.flipbook.loaded {
    display: block;
    opacity: 1;
    transform: translateY(0);
}

/* Styles for pages injected by JS */
.page {
    background-color: white;
    overflow: hidden;
    /* Optional paper texture or slight border */
    /* border-right: 1px solid rgba(0,0,0,0.05); */
}

.page-content {
    width: 100%;
    height: 100%;
    object-fit: contain;
}

/* Canvas specifically */
canvas.page-content {
    display: block;
    width: 100%;
    height: 100%;
}

/* Controls */
.controls {
    position: absolute;
    bottom: 2rem;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    align-items: center;
    gap: 1.5rem;
    padding: 0.75rem 1.5rem;
    background: var(--glass-bg);
    border: 1px solid var(--glass-border);
    backdrop-filter: blur(12px);
    border-radius: 2rem;
    box-shadow: var(--shadow-gentle);
    z-index: 20;
}

.btn {
    background: transparent;
    border: none;
    cursor: pointer;
    color: #475569;
    padding: 0.5rem;
    border-radius: 50%;
    transition: all 0.2s;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn:hover {
    background: rgba(37, 99, 235, 0.1);
    color: var(--primary-color);
}

.btn:active {
    transform: scale(0.95);
}

#pageInfo {
    font-variant-numeric: tabular-nums;
    font-weight: 500;
    color: #334155;
    font-size: 0.9rem;
}

/* Responsive adjustments */
@media (max-width: 768px) {
    .app-header {
        top: 1rem;
    }
    .app-header h1 {
        font-size: 1.25rem;
    }
    .controls {
        bottom: 1.5rem;
        padding: 0.5rem 1rem;
        width: 90%; /* wider on mobile */
        justify-content: space-between;
    }
}