:root {
    /* Color Palette - Premium Professional Look */
    --primary: #1a237e; /* Deep Navy */
    --primary-light: #534bae;
    --primary-dark: #000051;
    --secondary: #c5a059; /* Muted Gold */
    --secondary-light: #f8d189;
    --secondary-dark: #94712d;
    --accent: #00e5ff;
    --bg-light: #f5f7fa;
    --bg-dark: #121212;
    --text-main: #2c3e50;
    --text-muted: #7f8c8d;
    --white: #ffffff;
    --success: #27ae60;
    --error: #e74c3c;
    --warning: #f1c40f;
    --info: #3498db;

    /* Shadows */
    --shadow-sm: 0 2px 4px rgba(0,0,0,0.1);
    --shadow-md: 0 4px 15px rgba(0,0,0,0.1);
    --shadow-lg: 0 10px 30px rgba(0,0,0,0.15);
    --shadow-inset: inset 0 2px 4px rgba(0,0,0,0.06);

    /* Transitions */
    --transition: all 0.3s cubic-bezier(0.25, 0.8, 0.25, 1);
    
    /* Layout */
    --container-width: 1200px;
    --radius-sm: 8px;
    --radius-md: 15px;
    --radius-lg: 25px;
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    line-height: 1.6;
    color: var(--text-main);
    background-color: var(--bg-light);
    overflow-x: hidden;
    -webkit-font-smoothing: antialiased;
}

/* Typography */
h1, h2, h3, h4 {
    font-weight: 700;
    line-height: 1.2;
    margin-bottom: 1rem;
    color: var(--primary-dark);
}

h1 { font-size: clamp(2rem, 5vw, 3rem); }
h2 { font-size: clamp(1.5rem, 4vw, 2.2rem); }
h3 { font-size: 1.5rem; }

p { margin-bottom: 1.5rem; }

/* Layout Components */
.container {
    max-width: var(--container-width);
    margin: 0 auto;
    padding: 0 2rem;
}

section {
    padding: 4rem 0;
}

/* Header & Navigation */
header {
    background: rgba(255, 255, 255, 0.8);
    backdrop-filter: blur(10px);
    position: sticky;
    top: 0;
    z-index: 1000;
    border-bottom: 1px solid rgba(0,0,0,0.05);
    height: 80px;
    display: flex;
    align-items: center;
}

.nav-container {
    display: flex;
    justify-content: space-between;
    align-items: center;
    width: 100%;
}

.logo {
    font-size: 1.5rem;
    font-weight: 800;
    color: var(--primary);
    text-decoration: none;
    letter-spacing: -1px;
}

.logo span { color: var(--secondary); }

.nav-links {
    display: flex;
    gap: 2rem;
}

.nav-links a {
    text-decoration: none;
    color: var(--text-main);
    font-weight: 500;
    font-size: 0.95rem;
    transition: var(--transition);
}

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

/* Breadcrumbs */
.breadcrumbs {
    padding: 1rem 0;
    font-size: 0.85rem;
    color: var(--text-muted);
}

.breadcrumbs a {
    color: var(--primary);
    text-decoration: none;
}

.breadcrumbs span { margin: 0 0.5rem; }

/* Cards (Grid Style) */
.card-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 2rem;
}

.content-card {
    background: var(--white);
    border-radius: var(--radius-md);
    padding: 2rem;
    box-shadow: var(--shadow-md);
    transition: var(--transition);
    border: 1px solid rgba(0,0,0,0.03);
    cursor: pointer;
    display: flex;
    flex-direction: column;
    text-decoration: none;
    color: inherit;
}

.content-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-lg);
    border-color: var(--secondary-light);
}

.content-card .chapter-badge {
    background: var(--primary-light);
    color: var(--white);
    padding: 0.2rem 0.8rem;
    border-radius: 20px;
    font-size: 0.75rem;
    font-weight: 600;
    align-self: flex-start;
    margin-bottom: 1rem;
}

/* Interactive Components Styles */

/* Flip Cards */
.flip-card-container {
    perspective: 1000px;
    height: 300px;
    margin-bottom: 2rem;
}

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

.flip-card.flipped {
    transform: rotateY(180deg);
}

.flip-card-front, .flip-card-back {
    position: absolute;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: var(--radius-md);
    padding: 2rem;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    text-align: center;
    box-shadow: var(--shadow-md);
}

.flip-card-front {
    background: var(--white);
    border-left: 5px solid var(--secondary);
}

.flip-card-back {
    background: var(--primary);
    color: var(--white);
    transform: rotateY(180deg);
}

/* Interactive Forms & Quizzes */
.interactive-section {
    background: var(--white);
    padding: 3rem;
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    margin: 2rem 0;
}

.input-group {
    margin-bottom: 1.5rem;
}

.input-group label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 600;
}

input[type="text"], input[type="number"], select {
    width: 100%;
    padding: 0.8rem 1rem;
    border: 2px solid #e0e6ed;
    border-radius: var(--radius-sm);
    font-size: 1rem;
    transition: var(--transition);
}

input:focus {
    border-color: var(--primary-light);
    outline: none;
    box-shadow: 0 0 0 4px rgba(83, 75, 174, 0.1);
}

.btn {
    display: inline-block;
    padding: 1rem 2rem;
    border-radius: var(--radius-sm);
    font-weight: 700;
    text-transform: uppercase;
    letter-spacing: 1px;
    cursor: pointer;
    transition: var(--transition);
    border: none;
    font-size: 0.9rem;
}

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

.btn-primary:hover {
    background: var(--primary-dark);
    transform: scale(1.02);
}

.feedback {
    margin-top: 1rem;
    padding: 1rem;
    border-radius: var(--radius-sm);
    display: none;
}

.feedback.correct {
    display: block;
    background: #d4edda;
    color: #155724;
    border-left: 4px solid var(--success);
}

.feedback.incorrect {
    display: block;
    background: #f8d7da;
    color: #721c24;
    border-left: 4px solid var(--error);
}

/* Calculator & Simulators */
.simulator-container {
    background: #f8f9fa;
    padding: 2rem;
    border-radius: var(--radius-md);
    border: 1px solid #e9ecef;
}

.equation-display {
    display: flex;
    justify-content: center;
    align-items: center;
    gap: 1rem;
    font-size: 1.8rem;
    font-weight: 800;
    margin: 2rem 0;
    flex-wrap: wrap;
}

.equation-part {
    padding: 1rem 2rem;
    background: var(--white);
    border-radius: var(--radius-sm);
    box-shadow: var(--shadow-sm);
    min-width: 150px;
    text-align: center;
}

/* T-Account Styles */
.t-account {
    border-top: 2px solid var(--primary-dark);
    text-align: center;
}

.t-account-header {
    font-weight: 800;
    padding: 0.5rem;
    border-bottom: 2px solid var(--primary-dark);
}

.t-account-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    min-height: 200px;
}

.t-account-side {
    padding: 1rem;
}

.t-account-side.left {
    border-right: 1px solid var(--primary-dark);
}

/* Animations */
@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

.animate-fade-in {
    animation: fadeIn 0.8s ease-out forwards;
}

/* Responsive Table */
.table-scroll {
    overflow-x: auto;
    margin: 1rem 0;
}

table {
    width: 100%;
    border-collapse: collapse;
    background: var(--white);
}

th, td {
    padding: 1rem;
    border-bottom: 1px solid #eee;
    text-align: left;
}

th {
    background: var(--bg-light);
    color: var(--primary-dark);
    font-weight: 700;
}

/* Financial Statement Text Styling */
.text-right { text-align: right; }
.text-center { text-align: center; }
.indent-1 { padding-left: 2rem !important; }
.indent-2 { padding-left: 4rem !important; }

/* Financial Tables Specifics */
.financial-table {
    border: none;
    margin-bottom: 2rem;
}

.financial-table th, .financial-table td {
    padding: 0.5rem 1rem;
    border: none;
}

.financial-table .border-top {
    border-top: 1px solid var(--primary-dark);
}

.financial-table .double-border-bottom {
    border-bottom: 3px double var(--primary-dark);
}

.financial-table .total-row {
    font-weight: 700;
}

.financial-statement-container {
    background: var(--white);
    padding: 2.5rem;
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-sm);
    margin: 2rem 0;
    max-width: 800px;
    margin-left: auto;
    margin-right: auto;
}

.statement-header {
    text-align: center;
    margin-bottom: 2rem;
}

.statement-header h4 {
    margin-bottom: 0.2rem;
    color: var(--primary-dark);
}

.statement-header p {
    font-style: italic;
    color: var(--text-muted);
    font-size: 0.9rem;
}

/* =====================
 * ENHANCED INTERACTIVE COMPONENTS
 * ===================== */

/* Depth Toggle for Tiered Learning */
.depth-toggle {
    display: flex;
    gap: 1rem;
    margin: 2rem 0;
    padding: 1rem;
    background: var(--bg-light);
    border-radius: var(--radius-sm);
    justify-content: center;
    flex-wrap: wrap;
}

.depth-btn {
    padding: 0.5rem 1.5rem;
    border: 2px solid var(--primary-light);
    background: var(--white);
    color: var(--primary);
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

.depth-btn:hover {
    background: var(--primary-light);
    color: var(--white);
}

.depth-btn.active {
    background: var(--primary);
    color: var(--white);
    border-color: var(--primary);
}

.depth-content {
    display: none;
    animation: fadeIn 0.3s ease-out;
}

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

/* Drag and Drop */
.drag-drop-container {
    margin: 2rem 0;
}

.draggable {
    padding: 1rem 1.5rem;
    background: var(--white);
    border: 2px solid var(--primary-light);
    border-radius: var(--radius-sm);
    margin: 0.5rem;
    cursor: grab;
    user-select: none;
    transition: var(--transition);
    display: inline-block;
    box-shadow: var(--shadow-sm);
}

.draggable:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.draggable.dragging {
    opacity: 0.5;
    cursor: grabbing;
}

.drop-zone {
    min-height: 100px;
    border: 2px dashed var(--primary-light);
    border-radius: var(--radius-md);
    padding: 1rem;
    margin: 1rem 0;
    display: flex;
    align-items: center;
    justify-content: center;
    background: var(--bg-light);
    transition: var(--transition);
}

.drop-zone.drag-over {
    border-color: var(--primary);
    background: var(--primary-light);
    background-opacity: 0.1;
}

.drop-zone.correct {
    border-color: var(--success);
    background: #d4edda;
}

.drop-zone.incorrect {
    border-color: var(--error);
    background: #f8d7da;
}

/* Step-by-Step Guidance */
.step-by-step {
    position: relative;
    padding: 2rem 0;
}

.step-content {
    display: none;
    animation: fadeIn 0.5s ease-out;
}

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

.step-nav {
    display: flex;
    justify-content: space-between;
    margin-top: 2rem;
    padding-top: 2rem;
    border-top: 2px solid var(--bg-light);
}

.step-progress {
    background: var(--primary);
    color: var(--white);
    padding: 0.5rem 1rem;
    border-radius: 20px;
    font-size: 0.9rem;
    font-weight: 600;
}

/* Flashcards */
.flashcard-deck {
    position: relative;
    min-height: 400px;
    margin: 2rem 0;
}

.flashcard {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 400px;
    background: var(--white);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-lg);
    perspective: 1000px;
    transform-style: preserve-3d;
    transition: transform 0.6s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    padding: 3rem;
    text-align: center;
    border: 4px solid var(--secondary);
}

.flashcard.flipped {
    background: var(--primary);
    color: var(--white);
}

.flashcard-controls {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-top: 2rem;
}

.flashcard-nav-btn {
    padding: 0.8rem 1.5rem;
    background: var(--bg-light);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

.flashcard-nav-btn:hover:not(:disabled) {
    background: var(--primary-light);
    color: var(--white);
}

.flashcard-nav-btn:disabled {
    opacity: 0.3;
    cursor: not-allowed;
}

.flashcard-flip {
    padding: 1rem 2rem;
    background: var(--secondary);
    color: var(--white);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 700;
    transition: var(--transition);
}

.flashcard-flip:hover {
    transform: scale(1.05);
    box-shadow: var(--shadow-md);
}

/* Timeline Animations */
.interactive-timeline {
    position: relative;
    padding: 3rem 0;
    margin: 2rem 0;
}

.timeline-item {
    opacity: 0.3;
    transform: translateX(-50px);
    transition: all 0.5s cubic-bezier(0.4, 0, 0.2, 1);
    padding: 1.5rem;
    background: var(--white);
    border-radius: var(--radius-md);
    border-left: 4px solid var(--primary);
    margin: 1rem 0;
}

.timeline-item.active {
    opacity: 1;
    transform: translateX(0);
    border-left-color: var(--secondary);
    box-shadow: var(--shadow-lg);
}

.timeline-controls {
    display: flex;
    justify-content: center;
    gap: 1rem;
    margin-top: 2rem;
}

.timeline-btn {
    padding: 0.8rem 1.5rem;
    background: var(--primary);
    color: var(--white);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 600;
    transition: var(--transition);
}

.timeline-btn:hover:not(:disabled) {
    background: var(--primary-dark);
    transform: scale(1.05);
}

.timeline-btn:disabled {
    background: var(--bg-light);
    color: var(--text-muted);
    cursor: not-allowed;
}

/* Knowledge Point Expanded Structure */
.kp-header {
    margin-bottom: 2rem;
    padding-bottom: 1rem;
    border-bottom: 3px solid var(--secondary);
}

.kp-section {
    margin: 3rem 0;
    padding: 2rem;
    background: var(--white);
    border-radius: var(--radius-md);
    box-shadow: var(--shadow-md);
}

.kp-section h2 {
    color: var(--primary);
    margin-bottom: 1.5rem;
    padding-left: 1rem;
    border-left: 4px solid var(--secondary);
}

.learning-objectives ul {
    list-style: none;
    padding-left: 0;
}

.learning-objectives li {
    padding: 0.8rem 0 0.8rem 2.5rem;
    position: relative;
    margin: 0.5rem 0;
    background: var(--bg-light);
    border-radius: var(--radius-sm);
}

.learning-objectives li:before {
    content: "✓";
    position: absolute;
    left: 1rem;
    color: var(--success);
    font-weight: 800;
}

.key-concepts-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
    gap: 1.5rem;
    margin: 1.5rem 0;
}

.concept-card {
    background: var(--bg-light);
    padding: 1.5rem;
    border-radius: var(--radius-sm);
    border-left: 4px solid var(--primary);
    transition: var(--transition);
}

.concept-card:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-md);
}

.concept-card strong {
    color: var(--primary);
    display: block;
    margin-bottom: 0.5rem;
}

.worked-example {
    background: linear-gradient(135deg, var(--bg-light) 0%, var(--white) 100%);
    padding: 2rem;
    border-radius: var(--radius-md);
    margin: 2rem 0;
    border: 2px solid var(--primary-light);
}

.worked-example h4 {
    color: var(--secondary);
    margin-bottom: 1rem;
}

.example-step {
    margin: 1rem 0;
    padding-left: 2rem;
    position: relative;
}

.example-step:before {
    content: counter(example-step-counter);
    counter-increment: example-step-counter;
    position: absolute;
    left: 0;
    width: 28px;
    height: 28px;
    background: var(--primary);
    color: var(--white);
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-weight: 700;
    font-size: 0.9rem;
}

.misconception-alert {
    background: #fff3cd;
    border-left: 4px solid var(--warning);
    padding: 1.5rem;
    margin: 1rem 0;
    border-radius: var(--radius-sm);
}

.professional-tip {
    background: #d1ecf1;
    border-left: 4px solid var(--info);
    padding: 1.5rem;
    margin: 1rem 0;
    border-radius: var(--radius-sm);
}

.interactive-simulator {
    background: var(--bg-dark);
    color: var(--white);
    padding: 2.5rem;
    border-radius: var(--radius-lg);
    margin: 2rem 0;
}

.simulator-result {
    background: var(--primary);
    padding: 1rem 2rem;
    border-radius: var(--radius-sm);
    display: inline-block;
    margin-top: 1rem;
    font-size: 1.5rem;
    font-weight: 800;
}

.memory-aid-card {
    background: linear-gradient(135deg, var(--secondary) 0%, var(--secondary-dark) 100%);
    color: var(--white);
    padding: 2rem;
    border-radius: var(--radius-md);
    margin: 1.5rem 0;
    box-shadow: var(--shadow-lg);
}

.memory-aid-card strong {
    display: block;
    font-size: 1.2rem;
    margin-bottom: 1rem;
}

.comparison-table {
    width: 100%;
    border-collapse: collapse;
    margin: 2rem 0;
}

.comparison-table th {
    background: var(--primary);
    color: var(--white);
    padding: 1rem;
    text-align: left;
}

.comparison-table td {
    background: var(--white);
    padding: 1rem;
    border-bottom: 2px solid var(--primary-light);
}

.comparison-table tr:hover td {
    background: var(--bg-light);
}

/* SVG Canvas Animations */
.svg-animation-canvas {
    width: 100%;
    height: auto;
    border-radius: var(--radius-md);
    background: var(--white);
    box-shadow: var(--shadow-sm);
    max-width: 800px;
    margin: 2rem auto;
    display: block;
}

/* Quiz Retry Button */
.quiz-retry {
    margin-top: 1rem;
    padding: 0.5rem 1.5rem;
    background: var(--warning);
    color: var(--text-main);
    border: none;
    border-radius: var(--radius-sm);
    cursor: pointer;
    font-weight: 600;
    display: none;
}

.quiz-retry:hover {
    background: var(--warning-dark);
    transform: scale(1.05);
}

.quiz-explanation {
    display: none;
    margin-top: 1rem;
    padding: 1rem;
    background: var(--bg-light);
    border-radius: var(--radius-sm);
    border-left: 4px solid var(--info);
}

.correct-animation {
    animation: successPulse 0.5s ease-out;
}

@keyframes successPulse {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); }
}

/* Journal Entry Simulator */
.journal-entry-template {
    display: none;
}

.journal-entries {
    margin: 2rem 0;
}

.journal-entry-row {
    display: grid;
    grid-template-columns: 100px 1fr 80px 120px 120px;
    gap: 0.5rem;
    padding: 0.8rem;
    background: var(--bg-light);
    border-radius: var(--radius-sm);
    margin: 0.5rem 0;
    align-items: center;
}

/* T-Account Calculator */
.taccount-calculator-inputs {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    margin: 2rem 0;
}

.taccount-balance-display {
    text-align: center;
    padding: 2rem;
    background: var(--primary);
    color: var(--white);
    border-radius: var(--radius-md);
    margin: 2rem 0;
}

.taccount-balance-display .amount {
    font-size: 2.5rem;
    font-weight: 800;
    margin: 1rem 0;
}

.taccount-balance-display .type {
    font-size: 1.2rem;
    font-weight: 600;
}

/* Mobile Responsive Adjustments */
@media (max-width: 768px) {
    .container { padding: 0 1rem; }
    .nav-links { display: none; }
    section { padding: 3rem 0; }
    .interactive-section { padding: 1.5rem; }
    .equation-display { font-size: 1.2rem; }
    .depth-toggle { flex-direction: column; }
    .key-concepts-grid { grid-template-columns: 1fr; }
    .journal-entry-row { grid-template-columns: 1fr; gap: 0.5rem; }
    .flashcard { height: 350px; }
    .flashcard-deck { min-height: 350px; }
}