:root {
    --primary: #6366f1;
    --primary-hover: #4f46e5;
    --primary-light: #e0e7ff;
    
    --secondary: #ec4899;
    --secondary-hover: #db2777;
    
    --success: #10b981;
    --success-bg: #d1fae5;
    
    --error: #ef4444;
    --error-bg: #fee2e2;
    
    --warning: #f59e0b;
    
    --surface-100: #ffffff;
    --surface-200: #f8fafc;
    --surface-300: #f1f5f9;
    
    --text-main: #0f172a;
    --text-muted: #64748b;
    --text-light: #94a3b8;
    
    --border: #e2e8f0;
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.05);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.1), 0 2px 4px -2px rgb(0 0 0 / 0.1);
    --shadow-lg: 0 10px 15px -3px rgb(0 0 0 / 0.1), 0 4px 6px -4px rgb(0 0 0 / 0.1);
    
    --radius-md: 0.5rem;
    --radius-lg: 1rem;
    --radius-full: 9999px;
    
    --font-heading: 'Noto Sans SC', sans-serif;
    --font-body: 'Inter', 'Noto Sans SC', sans-serif;
}

body.dark-mode {
    --primary: #818cf8;
    --primary-hover: #6366f1;
    --primary-light: rgba(99, 102, 241, 0.15);
    
    --secondary: #f472b6;
    
    --success: #34d399;
    --success-bg: rgba(16, 185, 129, 0.15);
    
    --error: #f87171;
    --error-bg: rgba(239, 68, 68, 0.15);
    
    --surface-100: #1e293b;
    --surface-200: #0f172a;
    --surface-300: #334155;
    
    --text-main: #f1f5f9;
    --text-muted: #94a3b8;
    --text-light: #64748b;
    
    --border: #334155;
    
    --shadow-sm: 0 1px 2px 0 rgb(0 0 0 / 0.3);
    --shadow-md: 0 4px 6px -1px rgb(0 0 0 / 0.3);
}

* {
    box-sizing: border-box;
}

body {
    font-family: var(--font-body);
    background-color: var(--surface-200);
    color: var(--text-main);
    margin: 0;
    line-height: 1.6;
    transition: background-color 0.3s ease, color 0.3s ease;
    -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4, h5, h6 {
    font-family: var(--font-heading);
    color: var(--text-main);
    margin-top: 0;
}

button {
    font-family: var(--font-body);
}

#sidebar {
    width: 280px;
    position: fixed;
    top: 0;
    left: 0;
    bottom: 0;
    background-color: var(--surface-100);
    border-right: 1px solid var(--border);
    padding: 1.5rem;
    overflow-y: auto;
    z-index: 50;
    transition: transform 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

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

::-webkit-scrollbar-track {
    background: transparent;
}

::-webkit-scrollbar-thumb {
    background-color: var(--border);
    border-radius: 4px;
    border: 2px solid transparent;
    background-clip: content-box;
}

::-webkit-scrollbar-thumb:hover {
    background-color: var(--text-light);
}

#sidebar::-webkit-scrollbar,
#right-sidebar::-webkit-scrollbar {
    width: 6px;
}

#main-content {
    margin-left: 280px;
    margin-right: 280px;
    padding: 2rem;
    min-height: 100vh;
    display: flex;
    justify-content: center;
}

.main-container {
    width: 100%;
    max-width: 900px;
    background: transparent;
    padding: 0;
    box-shadow: none;
}

h1#main-title {
    font-size: 1.75rem;
    font-weight: 700;
    text-align: center;
    color: var(--text-main);
    margin-bottom: 2rem;
    padding-bottom: 0;
    border-bottom: none;
    background: linear-gradient(135deg, var(--primary), var(--secondary));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.sidebar-header {
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--primary);
    margin-bottom: 1.5rem;
    padding-bottom: 0.5rem;
    border-bottom: 2px solid var(--primary-light);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.sidebar-header::before {
    content: '\f013';
    font-family: 'Font Awesome 6 Free';
    font-weight: 900;
}

.dark-mode-toggle {
    display: flex;
    align-items: center;
    justify-content: space-between;
    padding: 0.75rem 1rem;
    background-color: var(--surface-300);
    border-radius: var(--radius-md);
    margin-bottom: 1.5rem;
    font-weight: 500;
    color: var(--text-main);
}

.switch { position: relative; display: inline-block; width: 40px; height: 22px; }
.switch input { display: none; }
.slider { position: absolute; cursor: pointer; top: 0; left: 0; right: 0; bottom: 0; background-color: var(--text-muted); transition: .4s; border-radius: 22px; opacity: 0.5; }
.slider:before { position: absolute; content: ""; height: 16px; width: 16px; left: 3px; bottom: 3px; background-color: white; transition: .4s; border-radius: 50%; box-shadow: 0 1px 2px rgba(0,0,0,0.2); }
input:checked + .slider { background-color: var(--primary); opacity: 1; }
input:checked + .slider:before { transform: translateX(18px); }

.sidebar-section {
    margin-bottom: 1.5rem;
}

.sidebar-section h4 {
    font-size: 0.8rem;
    text-transform: uppercase;
    letter-spacing: 0.05em;
    color: var(--text-muted);
    margin-bottom: 0.75rem;
    padding-left: 0;
    border: none;
}

.sidebar-button, .chapter-type-button, .chapter-test-button, .chapter-wrong-button {
    width: 100%;
    padding: 0.6rem 1rem;
    margin-bottom: 0.5rem;
    border: 1px solid transparent;
    border-radius: var(--radius-md);
    background-color: transparent;
    color: var(--text-main);
    font-size: 0.9rem;
    font-weight: 500;
    text-align: left;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.sidebar-button:hover, .chapter-type-button:hover, .chapter-test-button:hover, .chapter-wrong-button:hover {
    background-color: var(--surface-300);
    color: var(--primary);
}

.sidebar-button.active, .chapter-type-button.active, .chapter-wrong-button.active {
    background-color: var(--primary-light);
    color: var(--primary);
    font-weight: 600;
}

.sidebar-button.fav { color: var(--secondary); }
.sidebar-button.fav:hover { background-color: rgba(236, 72, 153, 0.1); }

.sidebar-button.wrong { color: var(--error); }
.sidebar-button.wrong:hover { background-color: var(--error-bg); }

#chapter-nav-list details {
    margin-bottom: 0.5rem;
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    overflow: hidden;
    background-color: var(--surface-100);
}

#chapter-nav-list summary {
    padding: 0.75rem 1rem;
    cursor: pointer;
    font-weight: 600;
    font-size: 0.95rem;
    list-style: none;
    position: relative;
    transition: background-color 0.2s;
    color: var(--text-main);
}

#chapter-nav-list summary:hover {
    background-color: var(--surface-200);
}

#chapter-nav-list summary::after {
    content: '\f054';
    font-family: 'Font Awesome 6 Free';
    font-weight: 900;
    font-size: 0.8rem;
    position: absolute;
    right: 1rem;
    top: 50%;
    transform: translateY(-50%);
    transition: transform 0.2s;
    color: var(--text-light);
}

#chapter-nav-list details[open] > summary::after {
    transform: translateY(-50%) rotate(90deg);
}

.chapter-button-container {
    padding: 0.5rem;
    background-color: var(--surface-200);
    border-top: 1px solid var(--border);
    display: grid;
    grid-template-columns: 1fr;
    gap: 0.25rem;
}

.chapter-test-button {
    background-color: var(--primary);
    color: white !important;
    text-align: center;
    justify-content: center;
}
.chapter-test-button:hover {
    background-color: var(--primary-hover);
    color: white !important;
}

#global-controls {
    display: none;
    flex-wrap: wrap;
    gap: 0.75rem;
    justify-content: center;
    padding-bottom: 1.5rem;
    margin-bottom: 2rem;
    border-bottom: 1px solid var(--border);
}

#global-controls button, .action-button, .quiz-button {
    padding: 0.5rem 1rem;
    border: none;
    border-radius: var(--radius-full);
    font-size: 0.875rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.2s ease;
    display: inline-flex;
    align-items: center;
    gap: 0.4rem;
    box-shadow: var(--shadow-sm);
}

#global-controls button:hover, .action-button:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-md);
}

#global-controls button:active {
    transform: translateY(0);
}

#test-chapter-wrong-btn, #test-all-wrong-btn { background-color: var(--primary); color: white; }
#clear-chapter-wrong-answers-btn, #clear-all-wrong-answers-btn { background-color: var(--surface-100); color: var(--error); border: 1px solid var(--error); }
#toggle-favorites-btn { background-color: var(--surface-100); color: var(--secondary); border: 1px solid var(--secondary); }
#toggle-all-answers-btn { background-color: var(--surface-300); color: var(--text-main); }

.question-block {
    background-color: var(--surface-100);
    padding: 1.5rem;
    margin-bottom: 1.5rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
    border: 1px solid var(--border);
    transition: transform 0.2s, box-shadow 0.2s;
    animation: slideUp 0.3s ease-out;
    display: none;
}

.question-block.visible { display: block; }

.question-block:hover {
    box-shadow: var(--shadow-md);
}

.question-block p {
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 1rem;
    color: var(--text-main);
}

.question-block ul {
    list-style: none;
    padding: 0;
    margin: 1rem 0;
    display: grid;
    gap: 0.5rem;
}

.question-block li {
    padding: 0.75rem 1rem;
    background-color: var(--surface-200);
    border-radius: var(--radius-md);
    color: var(--text-main);
    font-weight: 500;
    font-size: 1rem;
    border: 1px solid transparent;
    transition: border-color 0.2s;
}

.question-block li:hover {
    border-color: var(--primary-light);
}

.action-buttons-container {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    gap: 0.75rem;
    margin-top: 1.5rem;
    padding-top: 1rem;
    border-top: 1px dashed var(--border);
}

.action-button {
    background-color: var(--surface-200);
    color: var(--text-muted);
    box-shadow: none;
}

.action-button.favorite-button.favorited {
    color: var(--secondary);
    background-color: rgba(236, 72, 153, 0.1);
}

.action-button.remove-wrong-answer-btn {
    color: var(--error);
    background-color: rgba(239, 68, 68, 0.1);
}

.answer-span {
    display: none;
    color: var(--success);
    font-weight: 700;
    margin-left: 0.5rem;
}

.explanation-span {
    display: none;
    margin-top: 0.75rem;
    padding: 1rem;
    background-color: var(--surface-300);
    border-radius: var(--radius-md);
    color: var(--text-muted);
    font-size: 0.9rem;
    width: 100%;
}

#quiz-modal {
    display: none;
    position: fixed;
    z-index: 1000;
    left: 0;
    top: 0;
    width: 100%;
    height: 100%;
    overflow: auto;
    background-color: rgba(15, 23, 42, 0.7);
    backdrop-filter: blur(4px);
    padding-top: 60px;
}

#quiz-container {
    background-color: var(--surface-100);
    margin: 5% auto;
    border: 1px solid var(--border);
    box-shadow: var(--shadow-lg);
    border-radius: var(--radius-lg);
    padding: 2rem;
    max-width: 700px;
    width: 95%;
}

#quiz-title {
    color: var(--primary);
    text-align: center;
    margin-bottom: 2rem;
}

#close-quiz {
    color: var(--text-muted);
    top: 1rem;
    right: 1.5rem;
    font-size: 2rem;
    line-height: 1;
}

#quiz-progress {
    font-size: 0.9rem;
    color: var(--text-light);
    font-weight: 600;
}

#quiz-options label {
    display: flex;
    align-items: center;
    padding: 1rem;
    margin-bottom: 0.75rem;
    border: 2px solid var(--border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all 0.2s;
    background-color: var(--surface-100);
}

#quiz-options label:hover {
    border-color: var(--primary-light);
    background-color: var(--surface-200);
}

#quiz-options label:has(input:checked) {
    border-color: var(--primary);
    background-color: var(--primary-light);
    color: var(--primary);
    font-weight: 600;
}

#quiz-options input {
    margin-right: 1rem;
    accent-color: var(--primary);
}

#quiz-feedback {
    margin-top: 1.5rem;
    padding: 1rem 1.5rem;
    border-radius: var(--radius-md);
    animation: fadeIn 0.3s ease;
}

#quiz-feedback.correct {
    background-color: var(--success-bg);
    color: #065f46;
    border: 1px solid var(--success);
}
body.dark-mode #quiz-feedback.correct { color: #d1fae5; }

#quiz-feedback.incorrect {
    background-color: var(--error-bg);
    color: #991b1b;
    border: 1px solid var(--error);
}
body.dark-mode #quiz-feedback.incorrect { color: #fee2e2; }

#submit-answer-btn { background-color: var(--primary); color: white; width: 100%; justify-content: center; margin-top: 1rem; font-size: 1rem; padding: 0.8rem;}
#next-question-btn { background-color: var(--primary); color: white; width: 100%; justify-content: center; margin-top: 1rem; font-size: 1rem; padding: 0.8rem;}

#menu-toggle {
    display: none;
    position: fixed;
    top: 1rem;
    left: 1rem;
    z-index: 100;
    width: 45px;
    height: 45px;
    border-radius: var(--radius-md);
    background-color: var(--surface-100);
    box-shadow: var(--shadow-md);
    border: 1px solid var(--border);
    flex-direction: column;
    justify-content: center;
    align-items: center;
    gap: 5px;
    cursor: pointer;
}

#menu-toggle span {
    width: 24px;
    height: 3px;
    background-color: var(--primary);
    border-radius: 2px;
    transition: all 0.3s;
}

#notepad-toggle {
    display: none;
    position: fixed;
    top: 1rem;
    right: 1rem;
    z-index: 100;
    width: 45px;
    height: 45px;
    border-radius: var(--radius-md);
    background-color: var(--surface-100);
    box-shadow: var(--shadow-md);
    border: 1px solid var(--border);
    justify-content: center;
    align-items: center;
    cursor: pointer;
    color: var(--primary);
    font-size: 1.2rem;
}

@media (max-width: 992px) {
    #sidebar {
        transform: translateX(-100%);
        box-shadow: var(--shadow-lg);
    }
    
    #main-content {
        margin-left: 0;
        margin-right: 0;
        padding: 4rem 1rem 1rem; 
    }

    body.sidebar-open #sidebar {
        transform: translateX(0);
    }
    
    #menu-toggle {
        display: flex;
    }

    body.sidebar-open #menu-toggle {
        display: none;
    }
}

@keyframes slideUp {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeIn {
    from { opacity: 0; }
    to { opacity: 1; }
}

#welcome-message p {
    color: var(--text-muted);
    font-size: 1.1rem;
}

#global-search:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 3px var(--primary-light);
}

.modal {
    display: none; 
    position: fixed; 
    z-index: 1000; 
    left: 0;
    top: 0;
    width: 100%; 
    height: 100%; 
    overflow: auto; 
    background-color: rgba(15, 23, 42, 0.7); 
    backdrop-filter: blur(4px);
    padding-top: 60px;
}

.modal-content {
    background-color: var(--surface-100);
    margin: 5% auto; 
    padding: 2rem;
    border: 1px solid var(--border);
    width: 90%; 
    max-width: 600px;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    position: relative;
    animation: slideUp 0.3s ease-out;
}

.close-modal {
    color: var(--text-muted);
    float: right;
    font-size: 28px;
    font-weight: bold;
    cursor: pointer;
}
.close-modal:hover { color: var(--text-main); }

#stats-table th { color: var(--text-muted); font-size: 0.9rem; }
#stats-table td { padding: 12px 10px; border-bottom: 1px solid var(--border); font-size: 0.95rem; }

.progress-bar-bg {
    width: 100%;
    background-color: var(--surface-300);
    height: 8px;
    border-radius: 4px;
    overflow: hidden;
}
.progress-bar-fill {
    height: 100%;
    background-color: var(--primary);
    border-radius: 4px;
}

#right-sidebar {
    width: 280px;
    background-color: var(--surface-100);
    border-left: 1px solid var(--border);
    padding: 20px;
    display: flex;
    flex-direction: column;
    height: 100vh;
    height: 100vh;
    position: fixed;
    top: 0;
    right: 0;
    overflow-y: auto;
    z-index: 40;
}

.notepad-container {
    flex: 1;
    display: flex;
    flex-direction: column;
    margin-top: 10px;
}

#notepad {
    flex: 1;
    width: 100%;
    resize: none;
    border: 1px solid var(--border);
    border-radius: var(--radius-md);
    padding: 15px;
    font-family: inherit;
    font-size: 0.95rem;
    line-height: 1.6;
    background-color: var(--surface-50);
    color: var(--text-main);
    transition: all 0.2s;
    outline: none;
}

#notepad:focus {
    border-color: var(--primary);
    box-shadow: 0 0 0 3px var(--primary-light);
    background-color: var(--surface-100);
}

.text-button {
    background: none;
    border: none;
    cursor: pointer;
    transition: color 0.2s;
}
.text-button:hover { color: var(--error) !important; }

body.has-wallpaper {
    background-size: cover;
    background-position: center;
    background-attachment: fixed;
    background-repeat: no-repeat;
}

body.has-wallpaper #sidebar,
body.has-wallpaper #right-sidebar {
    background-color: rgba(255, 255, 255, 0.75);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    border-right-color: rgba(255,255,255,0.3);
    border-left-color: rgba(255,255,255,0.3);
}

body.has-wallpaper.dark-mode #sidebar,
body.has-wallpaper.dark-mode #right-sidebar {
    background-color: rgba(30, 41, 59, 0.75);
    border-color: rgba(255,255,255,0.1);
}

body.has-wallpaper .question-block,
body.has-wallpaper .modal-content,
body.has-wallpaper #quiz-container,
body.has-wallpaper .chapter-button-container,
body.has-wallpaper #chapter-nav-list details,
body.has-wallpaper .explanation-span {
    background-color: rgba(255, 255, 255, 0.85);
    backdrop-filter: blur(8px);
    -webkit-backdrop-filter: blur(8px);
    border: 1px solid rgba(255,255,255,0.4);
}

body.has-wallpaper.dark-mode .question-block,
body.has-wallpaper.dark-mode .modal-content,
body.has-wallpaper.dark-mode #quiz-container,
body.has-wallpaper.dark-mode .chapter-button-container,
body.has-wallpaper.dark-mode #chapter-nav-list details,
body.has-wallpaper.dark-mode .explanation-span {
    background-color: rgba(30, 41, 59, 0.85);
    border-color: rgba(255,255,255,0.1);
}

body.has-wallpaper #main-title {
    text-shadow: 0 2px 4px rgba(0,0,0,0.1);
    background: none;
    -webkit-text-fill-color: var(--text-main);
    color: var(--text-main);
}

@media (max-width: 1100px) {
    #right-sidebar {
        /* display: none;  Removed display none to allow transform */
        transform: translateX(100%);
        box-shadow: var(--shadow-lg);
        z-index: 60; /* Higher than left sidebar */
    }
    
    body.right-sidebar-open #right-sidebar {
        transform: translateX(0);
    }

    #main-content {
        margin-right: 0;
    }

    #notepad-toggle {
        display: flex;
    }

    body.right-sidebar-open #notepad-toggle {
        display: none;
    }
}