:root {
    --primary-color: #3b82f6;
    --primary-hover: #2a71dc;
    --primary-color-rgb: 59, 130, 246;

    --secondary-color: #40a9ff;
    --green-color: #28a745;
    --green-hover: #218838;

    --background-dark: #1e1e1e;
    --background-dark-rgb: 30, 30, 30;
    --background-light: #282828;
    --background-light-rgb: 40, 40, 40;

    --text-light: #ffffff;
    --text-dark: #888;

    --dropdown-bg: #333;
    --dropdown-hover: #3a3a3a;
    --dropdown-border: #444;
    --dropdown-text: #f0f0f0;

    --border-radius: 8px;
    --transition-speed: 0.2s;

    --shadow: 0 2px 10px rgba(0,0,0,0.15);
    --shadow-hover: 0 4px 12px rgba(0,0,0,0.25);
}

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

body {
    font-family: 'Segoe UI', system-ui, -apple-system, sans-serif;
    height: 100vh; /* Fallback */
    height: 100dvh; /* Dynamic viewport height for mobile */
    display: flex;
    flex-direction: column;
    background: var(--background-dark);
    color: var(--text-light);
    -webkit-font-smoothing: antialiased;
    overscroll-behavior: none;
    overflow: hidden; /* Prevent body scroll */
}

header {
    background: #222;
    padding: 0 16px;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 10px;
    height: 48px; /* Compact fixed height */
    flex-shrink: 0;
    box-shadow: 0 1px 0 rgba(255,255,255,0.05);
    z-index: 10;
}

.header-info, .header-controls, .header-center {
    display: flex;
    gap: 8px;
    align-items: center;
    flex-wrap: wrap;
}

.header-center {
    margin: 0 auto;
}

.subject-badge {
    background: #333;
    color: var(--secondary-color);
    font-weight: 600;
    padding: 4px 12px;
    font-size: 13px;
    border-left: 3px solid var(--secondary-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    white-space: nowrap;
    letter-spacing: 0.3px;
}

.control-group {
    display: flex;
    align-items: center;
    gap: 4px;
    position: relative;
    z-index: 100;
}

.control-group label {
    color: var(--secondary-color);
    font-weight: 500;
    font-size: 13px;
    white-space: nowrap;
}

/* Fix for dropdown overlap issues */
.custom-dropdown.open {
    z-index: 100;
}

/* Custom Dropdown Styles */
.custom-dropdown {
    position: relative;
    min-width: 130px;
    user-select: none;
}

.dropdown-selected {
    background: var(--dropdown-bg);
    color: var(--dropdown-text);
    font-size: 13px;
    font-weight: 500;
    padding: 0 12px;
    height: 32px; /* Compact height */
    border-radius: var(--border-radius);
    border: 1px solid transparent;
    cursor: pointer;
    box-shadow: none;
    display: flex;
    align-items: center;
    justify-content: space-between;
    transition: all var(--transition-speed) ease;
    background: rgba(255,255,255,0.05);
}

.dropdown-selected:hover {
    background: rgba(255,255,255,0.1);
    border-color: rgba(255,255,255,0.1);
}

.custom-dropdown.open .dropdown-selected {
    border-color: var(--primary-color);
    background: rgba(255,255,255,0.1);
}

.dropdown-text {
    flex: 1;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
}

.dropdown-arrow {
    width: 12px;
    height: 12px;
    flex-shrink: 0;
    margin-left: 8px;
    transition: transform var(--transition-speed) ease;
}

.custom-dropdown.open .dropdown-arrow {
    transform: rotate(180deg);
}

.dropdown-options {
    position: absolute;
    top: calc(100% + 4px);
    left: 0;
    right: 0;
    background: var(--dropdown-bg);
    border: 1px solid rgba(255,255,255,0.1);
    border-radius: var(--border-radius);
    box-shadow: 0 10px 30px rgba(0,0,0,0.5);
    max-height: 200px;
    overflow-y: auto;
    z-index: 1000;
    opacity: 0;
    visibility: hidden;
    transform: translateY(-8px);
    transition: all 0.2s ease;
}

.custom-dropdown.open .dropdown-options {
    opacity: 1;
    visibility: visible;
    transform: translateY(0);
}

.dropdown-option {
    padding: 8px 12px;
    font-size: 13px;
    color: var(--dropdown-text);
    cursor: pointer;
    transition: background-color 0.15s ease;
}

.dropdown-option:hover {
    background: var(--dropdown-hover);
}

.dropdown-option.selected {
    background: var(--primary-color);
    color: var(--text-light);
    font-weight: 600;
}

.dropdown-option.disabled {
    opacity: 0.5;
    cursor: not-allowed;
    pointer-events: none;
}

.dropdown-options::-webkit-scrollbar {
    width: 6px;
}

.dropdown-options::-webkit-scrollbar-track {
    background: var(--dropdown-bg);
}

.dropdown-options::-webkit-scrollbar-thumb {
    background: #555;
    border-radius: 3px;
}

button {
    padding: 0 16px;
    height: 32px; /* Compact height */
    font-size: 13px;
    font-weight: 500;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    background: #444;
    color: var(--text-light);
    box-shadow: var(--shadow);
    display: flex;
    align-items: center;
    gap: 6px;
    transition: all var(--transition-speed) ease;
}

button:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-hover);
}

button:active {
    transform: translateY(0);
}

button.primary {
    background-color: var(--primary-color);
}

button.primary:hover {
    background-color: var(--primary-hover);
}

button.back {
    background-color: var(--green-color);
}

button.back:hover {
    background-color: var(--green-hover);
}

#pdf-container {
    flex: 1;
    display: grid;
    padding: 0;
    background: var(--background-light);
    overflow: hidden; /* Viewer handles internal scroll */
    position: relative;
}

.pdf-viewer {
    width: 100%;
    height: 100%;
    background: #2a2a2a;
    position: relative;
    display: flex;
    flex-direction: column;
    /* Removed contain: strict to allow dropdowns to pop out if needed, though overflow hidden usually clips */
}

.pdf-viewer iframe {
    width: 100%;
    height: 100%;
    border: none;
}

/* Redesigned Floating Paper Selector */
.paper-selector {
    position: absolute;
    bottom: 20px;
    left: 50%;
    transform: translateX(-50%);
    display: flex;
    align-items: center;
    gap: 8px;
    padding: 4px 6px 4px 16px;
    
    background: rgba(30, 30, 30, 0.85);
    backdrop-filter: blur(12px);
    -webkit-backdrop-filter: blur(12px);
    
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: 100px; /* Pill shape */
    box-shadow: 0 8px 32px rgba(0, 0, 0, 0.4);
    
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    opacity: 0.9;
    z-index: 100;
    max-width: 90%;
}

.paper-selector:hover,
.paper-selector:focus-within {
    opacity: 1;
    transform: translateX(-50%) translateY(-2px);
    box-shadow: 0 12px 40px rgba(0, 0, 0, 0.5);
    background: rgba(30, 30, 30, 0.95);
    border-color: rgba(255, 255, 255, 0.2);
}

.paper-selector-label {
    font-size: 12px;
    font-weight: 600;
    color: var(--secondary-color);
    text-transform: uppercase;
    letter-spacing: 0.5px;
    white-space: nowrap;
}

.paper-selector .custom-dropdown {
    min-width: 180px;
    max-width: 320px;
}

.paper-selector .dropdown-selected {
    background: transparent;
    border: none;
    padding: 0 12px;
    height: 32px;
    color: var(--text-light);
}

.paper-selector .dropdown-selected:hover {
    background: rgba(255,255,255,0.08);
    border-radius: 20px;
}

.paper-dropdown .dropdown-options {
    bottom: calc(100% + 12px);
    top: auto;
    left: 50%;
    transform: translateX(-50%) translateY(10px);
    width: 100%;
    min-width: 240px;
    border-radius: 12px;
    background: #252525;
    border: 1px solid rgba(255,255,255,0.1);
    box-shadow: 0 10px 40px rgba(0,0,0,0.5);
    opacity: 0;
    visibility: hidden;
    transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}

.paper-dropdown.open .dropdown-options {
    transform: translateX(-50%) translateY(0);
    opacity: 1;
    visibility: visible;
}

.loader-container {
    position: absolute;
    inset: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background: rgba(0, 0, 0, 0.4);
    z-index: 5;
}

.loader {
    width: 32px;
    height: 32px;
    border: 3px solid #f3f3f3;
    border-top: 3px solid var(--primary-color);
    border-radius: 50%;
    animation: spin 0.8s linear infinite;
}

@keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
}

.grid-1 { grid-template-columns: 1fr; }
.grid-2 { grid-template-columns: repeat(2, 1fr); }
.grid-3 { grid-template-columns: repeat(3, 1fr); }
.grid-4 { grid-template-columns: repeat(2, 1fr); grid-template-rows: repeat(2, 1fr); }

.icon {
    width: 16px;
    height: 16px;
    flex-shrink: 0;
}

.no-pdf-message, .no-more-papers {
    text-align: center;
    font-weight: 500;
}

.no-pdf-message {
    padding: 40px;
    font-size: 16px;
    color: var(--text-dark);
}

.no-more-papers {
    padding: 15px;
    font-size: 14px;
    color: var(--text-dark);
    background: rgba(255,255,255,0.05);
    border-radius: var(--border-radius);
    border: 1px solid rgba(255,255,255,0.1);
    margin: 8px;
}

@media (max-width: 768px) {
    header {
        height: auto;
        padding: 8px 12px;
        gap: 8px;
        flex-direction: row;
        flex-wrap: wrap;
    }

    .header-info {
        flex: 1;
        width: auto;
        order: 1;
        margin-bottom: 0;
    }

    .header-controls {
        width: auto;
        order: 2;
        margin-top: 0;
    }

    .header-center {
        width: 100%;
        order: 3;
        flex-direction: row;
        gap: 12px;
        margin-top: 4px;
    }

    .control-group {
        flex: 1;
        width: auto;
        flex-direction: column;
        align-items: flex-start;
        gap: 4px;
    }
    
    .control-group label {
        font-size: 11px;
        min-width: auto;
    }
    
    .custom-dropdown {
        width: 100%;
        min-width: 0;
    }
    
    .dropdown-selected {
        width: 100%;
        padding: 0 10px;
    }

    .paper-selector {
        bottom: calc(16px + env(safe-area-inset-bottom, 0px));
        padding: 4px 6px 4px 12px;
        width: auto;
        max-width: 95%;
    }
    
    .paper-selector .custom-dropdown {
        min-width: 140px;
    }
}

/* Extra small devices */
@media (max-width: 480px) {
    header {
        padding: 4px;
        gap: 4px;
    }
    
    .header-info {
        gap: 4px;
    }
    
    .subject-badge {
        font-size: 12px;
        padding: 3px 8px;
    }
    
    button.back {
        padding: 6px 8px;
        font-size: 12px;
    }
    
    button.back .icon {
        width: 14px;
        height: 14px;
    }
    
    .control-group label {
        font-size: 12px;
        min-width: 45px;
    }
    
    .dropdown-selected {
        padding: 8px 30px 8px 10px;
        font-size: 13px;
    }
    
    .dropdown-option {
        padding: 10px 12px;
        font-size: 13px;
    }
    
    .paper-selector {
        bottom: calc(12px + env(safe-area-inset-bottom, 0px));
    }
    
    .paper-selector-label {
        font-size: 11px;
    }
}

::-webkit-scrollbar {
    width: 8px;
    height: 8px;
}

::-webkit-scrollbar-track {
    background: var(--background-dark);
}

::-webkit-scrollbar-thumb {
    background: #444;
    border-radius: 4px;
}

::-webkit-scrollbar-thumb:hover {
    background: #555;
}

.seo-content {
    position: absolute !important;
    left: -10000px !important;
    width: 1px !important;
    height: 1px !important;
    overflow: hidden !important;
    clip: rect(1px, 1px, 1px, 1px) !important;
    white-space: nowrap !important;
}

.seo-content h1, .seo-content h2, .seo-content h3, .seo-content p {
    margin: 0 !important;
    padding: 0 !important;
}

/* Rotation Prompt Styles */
.rotation-prompt {
    position: fixed;
    inset: 0;
    background: rgba(0, 0, 0, 0.9);
    z-index: 2000;
    display: flex;
    align-items: center;
    justify-content: center;
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
}

.rotation-content {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 20px;
    color: var(--text-light);
    text-align: center;
    padding: 20px;
}

.rotation-icon {
    width: 64px;
    height: 64px;
    animation: rotate-device 2s infinite ease-in-out;
    color: var(--primary-color);
}

@keyframes rotate-device {
    0% { transform: rotate(0deg); }
    30% { transform: rotate(90deg); }
    70% { transform: rotate(90deg); }
    100% { transform: rotate(0deg); }
}