:root {
    --bg-color: #0f172a;
    --panel-bg: #1e293b;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --accent-color: #3b82f6;
    --accent-hover: #2563eb;
    --border-color: #334155;
    --success-color: #10b981;
    --transition-speed: 0.3s;
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-primary);
    line-height: 1.6;
    height: 100vh;
    overflow: hidden;
    display: flex;
    flex-direction: column;
}

/* Navbar */
.navbar {
    background-color: var(--panel-bg);
    padding: calc(1rem + env(safe-area-inset-top)) 2rem 1rem 2rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
    border-bottom: 1px solid var(--border-color);
    flex-shrink: 0;
    z-index: 100;
}

.logo {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--accent-color);
}

.nav-links {
    list-style: none;
    display: flex;
    gap: 2rem;
}

.nav-links a {
    color: var(--text-secondary);
    text-decoration: none;
    font-weight: 600;
    transition: color var(--transition-speed);
}

.nav-links a:hover, .nav-links a.active {
    color: var(--text-primary);
}

.mobile-toggle {
    display: none;
    background: transparent;
    border: 1px solid var(--border-color);
    color: var(--text-primary);
    font-size: 1.2rem;
    cursor: pointer;
    padding: 0.5rem 0.75rem;
    border-radius: 4px;
    z-index: 1100;
}

.mobile-overlay {
    display: none;
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background-color: rgba(0, 0, 0, 0.5);
    z-index: 999;
    opacity: 0;
    transition: opacity 0.3s ease;
}

.mobile-overlay.active {
    display: block;
    opacity: 1;
}

/* Main Layout Grid */
.layout-container {
    display: flex;
    flex: 1;
    width: 100%;
    overflow: hidden;
}

/* 1. Left Sidebar Navigation */
.sidebar-nav {
    width: 320px;
    background-color: var(--panel-bg);
    padding: 1.5rem;
    border-right: 1px solid var(--border-color);
    flex-shrink: 0;
    overflow-y: auto;
}

.sidebar-title {
    font-size: 1.2rem;
    margin-bottom: 1.5rem;
    color: var(--text-primary);
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}

.nav-group {
    margin-bottom: 0.5rem;
}

.nav-group-header {
    display: flex;
    align-items: stretch;
    border-radius: 6px;
    transition: background-color var(--transition-speed);
}

.nav-group-header:hover {
    background-color: rgba(255, 255, 255, 0.05);
}

.nav-toggle-btn {
    background: none;
    border: none;
    color: var(--text-secondary);
    padding: 0.75rem 0.5rem 0.75rem 0.75rem;
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
}

.nav-toggle-btn .arrow {
    font-size: 0.8rem;
    transition: transform var(--transition-speed);
    transform: rotate(-90deg);
}

.nav-toggle-btn.active .arrow {
    transform: rotate(0);
}

.nav-link.chapter-link, .nav-link.sub-link {
    flex: 1;
    text-align: left;
    background: none;
    border: none;
    color: var(--text-primary);
    font-size: 1rem;
    font-weight: 600;
    padding: 0.75rem 0.75rem 0.75rem 0.25rem;
    cursor: pointer;
    text-decoration: none;
    font-family: inherit;
    display: flex;
    align-items: center;
}

.nav-link.chapter-link:hover, .nav-link.chapter-link.current,
.nav-link.sub-link:hover, .nav-link.sub-link.current {
    color: var(--accent-color);
}

/* Sub-Navigation */
.sub-group {
    border-bottom: none;
    margin-bottom: 0;
}
.nav-link.sub-link {
    font-size: 0.95rem;
    font-weight: 400;
    color: var(--text-secondary);
}
.sub-content {
    padding-left: 1rem;
}
.sub-content a {
    font-size: 0.9rem;
    padding: 0.5rem 1rem 0.5rem 1.5rem;
}

.nav-content {
    display: none;
    flex-direction: column;
    padding-left: 1rem;
    margin-top: 0.25rem;
}

.nav-content.active-content {
    display: flex;
}

.nav-content a {
    color: var(--text-secondary);
    text-decoration: none;
    padding: 0.5rem 0.75rem;
    border-radius: 4px;
    font-size: 0.9rem;
    transition: all var(--transition-speed);
    border-left: 2px solid transparent;
}

.nav-content a:hover {
    color: var(--text-primary);
    background-color: rgba(255, 255, 255, 0.05);
}

.nav-content a.current {
    color: var(--accent-color);
    border-left-color: var(--accent-color);
    background-color: rgba(59, 130, 246, 0.1);
}

/* 2. Main Reading Content (Natural Flow) */
.reading-content {
    flex: 1;
    background-color: transparent;
    padding: 0;
    overflow-y: auto;
    display: flex;
    flex-direction: column;
}

.reading-header {
    margin-bottom: 0;
    padding: 2rem 4rem 1rem 4rem;
    border-bottom: 1px solid var(--border-color);
}

.reading-header h1 {
    font-size: 2.2rem;
    color: var(--text-primary);
}

.markdown-body {
    padding: 0 4rem 2rem 4rem;
    flex: 1;
    display: flex;
    flex-direction: column;
}

.markdown-body h2 {
    color: var(--accent-color);
    margin-top: 2rem;
    margin-bottom: 1rem;
    font-size: 1.6rem;
}

.markdown-body h2:first-child {
    margin-top: 0;
}

.markdown-body p {
    color: var(--text-secondary);
    margin-bottom: 1.2rem;
    font-size: 1.05rem;
}

.markdown-body ul {
    margin-left: 1.5rem;
    margin-bottom: 1.5rem;
    color: var(--text-secondary);
}

.markdown-body li {
    margin-bottom: 0.5rem;
}

/* 3. Right Side Panel */
.study-panel {
    width: 380px;
    display: flex;
    flex-direction: column;
    gap: 1.5rem;
    background-color: var(--panel-bg);
    border-left: 1px solid var(--border-color);
    padding: 1.5rem;
    padding: 1.5rem;
    flex-shrink: 0;
    overflow-y: auto;
}

.panel-section {
    background-color: var(--bg-color);
    border-radius: 12px;
    padding: 1.5rem;
    border: 1px solid var(--border-color);
}

/* Quick Overview */
.quick-overview h3 {
    font-size: 1.2rem;
    margin-bottom: 1rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
    border-bottom: 1px solid var(--border-color);
    padding-bottom: 0.5rem;
}

.quick-overview h4 {
    color: var(--accent-color);
    margin-bottom: 0.5rem;
    font-size: 1rem;
    flex-shrink: 0;
}

#overview-list {
    margin: 0;
}

.quick-overview ul {
    list-style-type: none;
}

.quick-overview li {
    position: relative;
    padding-left: 1.5rem;
    margin-bottom: 0.5rem;
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.quick-overview li::before {
    content: "•";
    color: var(--accent-color);
    font-weight: bold;
    position: absolute;
    left: 0;
    font-size: 1.2rem;
}

/* Merged Tabs Section */
.interactive-review {
    padding: 0; /* Remove padding to make tabs edge-to-edge */
}

.tabs-header {
    display: flex;
    border-bottom: 1px solid var(--border-color);
    background-color: rgba(0,0,0,0.2);
}

.tab-btn {
    flex: 1;
    background: none;
    border: none;
    color: var(--text-secondary);
    padding: 1rem;
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: all var(--transition-speed);
    font-family: inherit;
    border-bottom: 2px solid transparent;
}

.tab-btn:hover {
    color: var(--text-primary);
    background-color: rgba(255,255,255,0.02);
}

.tab-btn.active {
    color: var(--accent-color);
    border-bottom-color: var(--accent-color);
    background-color: var(--bg-color);
}

.tab-content {
    display: none;
    padding: 1.5rem;
}

.tab-content.active {
    display: block;
}

/* Review Questions */
.question-card {
    background-color: var(--bg-color);
    padding: 1.2rem;
    border-radius: 8px;
    margin-bottom: 1rem;
    border: 1px solid rgba(255,255,255,0.05);
}

.question-card p {
    font-size: 0.95rem;
    margin-bottom: 1rem;
    font-weight: 500;
}

.btn-reveal {
    background-color: var(--border-color);
    color: var(--text-primary);
    border: none;
    padding: 0.6rem 1rem;
    border-radius: 6px;
    cursor: pointer;
    font-size: 0.85rem;
    transition: background-color var(--transition-speed);
    width: 100%;
    font-weight: 600;
}

.btn-reveal:hover {
    background-color: var(--accent-hover);
}

.answer-text {
    display: none;
    margin-top: 1rem;
    padding-top: 1rem;
    border-top: 1px dashed var(--border-color);
    color: var(--success-color);
    font-size: 0.9rem;
    animation: fadeIn 0.3s ease-in-out;
}

.answer-text.show {
    display: block;
}

/* Flashcards */
.mt-3 {
    margin-top: 1rem;
}

.flashcard {
    background-color: transparent;
    height: 160px;
    perspective: 1000px;
}

.flashcard-inner {
    position: relative;
    width: 100%;
    height: 100%;
    text-align: center;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    transform-style: preserve-3d;
    cursor: pointer;
}

.flashcard:hover .flashcard-inner {
    transform: rotateY(180deg);
}

.flashcard-front, .flashcard-back {
    position: absolute;
    width: 100%;
    height: 100%;
    -webkit-backface-visibility: hidden;
    backface-visibility: hidden;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    border-radius: 8px;
    padding: 1.5rem;
    border: 1px solid var(--border-color);
}

.flashcard-front {
    background-color: var(--bg-color);
}

.flashcard-front p {
    font-size: 1.1rem;
    font-weight: 600;
    color: var(--accent-color);
}

.flashcard-front .hint {
    font-size: 0.75rem;
    color: var(--text-secondary);
    margin-top: 1rem;
    opacity: 0.7;
}

.flashcard-back {
    background-color: var(--accent-color);
    color: white;
    transform: rotateY(180deg);
    border-color: var(--accent-color);
}

.flashcard-back p {
    font-size: 1.2rem;
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(-5px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Responsive Layout */
@media (max-width: 1100px) {
    .mobile-toggle {
        display: block;
    }

    .nav-links {
        display: none; /* Hide standard nav links on mobile to save space */
    }

    /* Sidebars become fixed overlays */
    .sidebar-nav {
        position: fixed;
        top: 0;
        left: 0;
        height: 100vh;
        z-index: 1000;
        transform: translateX(-100%);
        transition: transform 0.3s ease;
        box-shadow: 2px 0 10px rgba(0,0,0,0.5);
    }
    
    .sidebar-nav.open {
        transform: translateX(0);
    }

    .study-panel {
        position: fixed;
        top: 0;
        right: 0;
        height: 100vh;
        z-index: 1000;
        transform: translateX(100%);
        transition: transform 0.3s ease;
        box-shadow: -2px 0 10px rgba(0,0,0,0.5);
        max-width: 85%; /* Don't take up entire screen if screen is very small */
    }

    .study-panel.open {
        transform: translateX(0);
    }
}

/* Carousel Styles */
.carousel-wrapper {
    display: flex;
    align-items: center;
    position: relative;
    width: 100%;
}

.carousel-container {
    display: flex;
    overflow-x: auto;
    scroll-snap-type: x mandatory;
    gap: 1rem;
    width: 100%;
    scrollbar-width: none; /* Firefox */
    scroll-behavior: smooth;
    padding: 0 5px; /* Prevent box-shadow clipping if any */
}

.carousel-container::-webkit-scrollbar {
    display: none;
}

.carousel-item {
    scroll-snap-align: center;
    flex: 0 0 100%;
    min-width: 100%;
}

.carousel-prev, .carousel-next {
    background-color: var(--panel-bg);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    border-radius: 50%;
    width: 36px;
    height: 36px;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    position: absolute;
    z-index: 10;
    transition: all var(--transition-speed);
}

.carousel-prev { left: -18px; }
.carousel-next { right: -18px; }

.carousel-prev:hover, .carousel-next:hover {
    background-color: var(--accent-color);
    color: white;
}

/* Section Navigation Buttons */
.section-nav {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
    padding: 15px;
    margin: 15px 0;
    background-color: var(--panel-bg);
    border: 1px solid var(--border-color);
    border-radius: 8px;
    cursor: pointer;
    font-weight: 600;
    color: var(--accent-color);
    transition: opacity 0.3s ease, background-color 0.2s, color 0.2s;
    z-index: 10;
    opacity: 0;
    pointer-events: none;
}
.section-nav.top {
    position: sticky;
    top: 15px;
    box-shadow: 0 4px 15px rgba(0,0,0,0.4);
}
.section-nav.bottom {
    position: sticky;
    bottom: 15px;
    box-shadow: 0 -4px 15px rgba(0,0,0,0.4);
}
.section-nav:hover {
    background-color: rgba(59, 130, 246, 0.1);
}
.section-nav.end {
    cursor: default;
    color: var(--text-secondary);
}
.section-nav.end:hover {
    background-color: var(--panel-bg);
}
.subsection-content {
    animation: fadeIn 0.3s ease;
    flex: 1;
    padding: 10px 0;
}
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

/* Editor Styles */
.panel-header-flex {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 10px;
}
.btn-edit {
    background-color: var(--accent-color);
    color: white;
    border: none;
    padding: 6px 12px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 0.85rem;
    font-weight: 600;
    transition: background 0.2s;
}
.btn-edit:hover { background-color: #3b82f6; }
.btn-edit.editing { background-color: #ef4444; }
.btn-edit.editing:hover { background-color: #dc2626; }

.edit-textarea, .edit-q-input, .edit-a-input, .edit-f-front, .edit-f-back {
    width: 100%;
    background: var(--bg-color);
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    border-radius: 4px;
    padding: 8px;
    margin-bottom: 10px;
    font-family: 'Inter', sans-serif;
}
.edit-textarea { resize: vertical; }

.edit-group {
    background: rgba(0,0,0,0.2);
    padding: 10px;
    border-radius: 6px;
    margin-bottom: 15px;
    border: 1px solid var(--border-color);
}
.edit-group label {
    display: block;
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: 4px;
}
.btn-delete {
    background-color: transparent;
    color: #ef4444;
    border: 1px solid #ef4444;
    padding: 4px 8px;
    border-radius: 4px;
    font-size: 0.8rem;
    cursor: pointer;
}
.btn-delete:hover { background-color: #ef4444; color: white; }
.btn-add {
    background-color: var(--panel-bg);
    color: var(--accent-color);
    border: 1px dashed var(--accent-color);
    padding: 8px;
    width: 100%;
    border-radius: 6px;
    cursor: pointer;
    font-weight: 600;
}
.btn-add:hover { background-color: rgba(59, 130, 246, 0.1); }


/* GitHub Alerts */
.markdown-alert {
    padding: 1rem;
    margin-bottom: 1.5rem;
    border-left: 4px solid var(--accent-color);
    background-color: var(--card-bg);
    border-radius: 0 0.5rem 0.5rem 0;
    color: var(--text-secondary);
    font-size: 0.95rem;
    box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}
.markdown-alert p:last-child {
    margin-bottom: 0;
}
.markdown-alert-title {
    font-weight: 700;
    margin-top: 0;
    margin-bottom: 0.5rem;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}
.markdown-alert-note {
    border-left-color: #3b82f6;
}
.markdown-alert-note .markdown-alert-title {
    color: #3b82f6;
}
.markdown-alert-tip {
    border-left-color: #10b981;
}
.markdown-alert-tip .markdown-alert-title {
    color: #10b981;
}
.markdown-alert-important {
    border-left-color: #8b5cf6;
}
.markdown-alert-important .markdown-alert-title {
    color: #8b5cf6;
}
.markdown-alert-warning {
    border-left-color: #f59e0b;
}
.markdown-alert-warning .markdown-alert-title {
    color: #f59e0b;
}
.markdown-alert-caution {
    border-left-color: #ef4444;
}
.markdown-alert-caution .markdown-alert-title {
    color: #ef4444;
}

/* Edit Markdown Button */
.btn-edit-md {
    position: absolute;
    top: 1rem;
    right: 1rem;
    background-color: var(--accent-color);
    color: white;
    border: none;
    padding: 0.5rem 1rem;
    border-radius: 0.5rem;
    cursor: pointer;
    font-weight: 600;
    font-size: 0.8rem;
    z-index: 50;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}
.btn-edit-md:hover {
    background-color: #2563eb;
}
.edit-md-textarea {
    width: 100%;
    min-height: 70vh;
    background-color: var(--card-bg);
    color: var(--text-primary);
    border: 1px solid rgba(255, 255, 255, 0.1);
    border-radius: 0.5rem;
    padding: 1.5rem;
    font-family: monospace;
    font-size: 0.95rem;
    line-height: 1.5;
    resize: vertical;
}

.reading-content { position: relative; }

.markdown-body img {
    max-width: 100%;
    height: auto;
    border-radius: 8px;
    margin: 1rem 0;
    box-shadow: 0 4px 6px rgba(0,0,0,0.1);
}