:root {
    --primary-color: #6366f1;
    --secondary-color: #f43f5e;
    --accent-color: #10b981;
    --bg-color: #f8fafc;
    --card-bg: #ffffff;
    --text-color: #1f2937;
    --text-secondary: #6b7280;
    --border-color: #e5e7eb;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
}

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

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    line-height: 1.6;
}

header {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    text-align: center;
    padding: 2rem 1rem;
    box-shadow: var(--shadow);
}

header h1 {
    font-size: 2.5rem;
    font-weight: 700;
    margin-bottom: 0.5rem;
}

header p {
    font-size: 1.1rem;
    opacity: 0.9;
}

.tab-nav {
    display: flex;
    background: var(--card-bg);
    box-shadow: var(--shadow);
    overflow-x: auto;
}

.tab-btn {
    flex: 1;
    padding: 1rem 2rem;
    border: none;
    background: transparent;
    color: var(--text-secondary);
    font-weight: 500;
    cursor: pointer;
    transition: all 0.3s ease;
    border-bottom: 3px solid transparent;
    white-space: nowrap;
}

.tab-btn:hover {
    background: #f1f5f9;
    color: var(--primary-color);
}

.tab-btn.active {
    color: var(--primary-color);
    border-bottom-color: var(--primary-color);
    background: #f1f5f9;
}

.tab-content {
    display: none;
    padding: 2rem;
    max-width: 1200px;
    margin: 0 auto;
}

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

/* Venn Diagram Styles */
.venn-container {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
    align-items: start;
}

.controls {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.controls h3 {
    color: var(--primary-color);
    margin-bottom: 1.5rem;
    font-size: 1.5rem;
}

.set-controls {
    margin-bottom: 2rem;
}

.set-input {
    display: flex;
    align-items: center;
    gap: 1rem;
    margin-bottom: 1rem;
}

.set-input label {
    font-weight: 500;
    min-width: 80px;
}

.set-input input {
    flex: 1;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    transition: border-color 0.3s ease;
}

.set-input input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.set-color {
    width: 20px;
    height: 20px;
    border-radius: 50%;
    border: 2px solid white;
    box-shadow: 0 2px 4px rgba(0,0,0,0.2);
}

.operation-controls h4 {
    margin-bottom: 1rem;
    color: var(--text-color);
}

.operation-buttons {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(120px, 1fr));
    gap: 0.5rem;
    margin-bottom: 1.5rem;
}

.op-btn {
    padding: 0.75rem 1rem;
    border: 2px solid var(--border-color);
    background: white;
    color: var(--text-color);
    border-radius: 8px;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s ease;
    font-size: 0.9rem;
}

.op-btn:hover {
    border-color: var(--primary-color);
    background: #f8fafc;
}

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

.update-btn {
    width: 100%;
    padding: 1rem;
    background: var(--accent-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.3s ease;
}

.update-btn:hover {
    background: #059669;
}

.venn-diagram {
    background: var(--card-bg);
    border-radius: 12px;
    box-shadow: var(--shadow);
    padding: 2rem;
    text-align: center;
}

#vennSvg {
    border: 2px solid var(--border-color);
    border-radius: 8px;
    background: white;
    margin-bottom: 1rem;
}

.result-display {
    background: #f8fafc;
    padding: 1rem;
    border-radius: 8px;
    margin-top: 1rem;
}

.result-display h4 {
    color: var(--primary-color);
    margin-bottom: 0.5rem;
}

#operationResult {
    font-family: monospace;
    font-size: 1.1rem;
    color: var(--text-color);
    background: white;
    padding: 1rem;
    border-radius: 6px;
    border: 1px solid var(--border-color);
}

/* Operations Calculator Styles */
.operations-container {
    max-width: 800px;
    margin: 0 auto;
}

.calculator {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.calc-inputs {
    margin-bottom: 2rem;
}

.input-group {
    margin-bottom: 1rem;
}

.input-group label {
    display: block;
    font-weight: 500;
    margin-bottom: 0.5rem;
    color: var(--text-color);
}

.input-group input {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    font-size: 1rem;
    transition: border-color 0.3s ease;
}

.input-group input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.calc-operations {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 1rem;
    margin-bottom: 2rem;
}

.calc-btn {
    padding: 1rem;
    border: 2px solid var(--primary-color);
    background: white;
    color: var(--primary-color);
    border-radius: 8px;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s ease;
    font-size: 1rem;
}

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

.calc-results {
    background: #f8fafc;
    padding: 1.5rem;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

.calc-results h4 {
    color: var(--primary-color);
    margin-bottom: 1rem;
}

#calcResults {
    font-family: monospace;
    white-space: pre-line;
    background: white;
    padding: 1rem;
    border-radius: 6px;
    border: 1px solid var(--border-color);
    min-height: 100px;
}

/* Problems Styles */
.problems-container {
    max-width: 900px;
    margin: 0 auto;
}

.difficulty-selector {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    justify-content: center;
}

.diff-btn {
    padding: 0.75rem 2rem;
    border: 2px solid var(--border-color);
    background: white;
    color: var(--text-color);
    border-radius: 8px;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s ease;
}

.diff-btn:hover {
    border-color: var(--primary-color);
}

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

.problem-display {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

#currentProblem h4 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.3rem;
}

#problemText {
    margin-bottom: 1rem;
    font-size: 1.1rem;
    line-height: 1.6;
}

#problemSets {
    background: #f8fafc;
    padding: 1rem;
    border-radius: 8px;
    margin-bottom: 2rem;
    font-family: monospace;
    border: 1px solid var(--border-color);
}

.answer-section {
    margin-bottom: 2rem;
}

.answer-section label {
    display: block;
    font-weight: 500;
    margin-bottom: 0.5rem;
}

.answer-section input {
    width: 100%;
    padding: 0.75rem;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    margin-bottom: 1rem;
    font-size: 1rem;
}

.answer-section input:focus {
    outline: none;
    border-color: var(--primary-color);
}

.answer-section button {
    padding: 0.75rem 1.5rem;
    margin-right: 1rem;
    border: none;
    border-radius: 8px;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s ease;
}

#checkAnswer {
    background: var(--accent-color);
    color: white;
}

#checkAnswer:hover {
    background: #059669;
}

#showSolution {
    background: var(--secondary-color);
    color: white;
}

#showSolution:hover {
    background: #e11d48;
}

.feedback {
    padding: 1rem;
    border-radius: 8px;
    margin-bottom: 1rem;
    font-weight: 500;
}

.feedback.correct {
    background: #dcfce7;
    color: #166534;
    border: 1px solid #bbf7d0;
}

.feedback.incorrect {
    background: #fef2f2;
    color: #dc2626;
    border: 1px solid #fecaca;
}

.solution {
    background: #fffbeb;
    border: 1px solid #fed7aa;
    padding: 1.5rem;
    border-radius: 8px;
    margin-bottom: 1rem;
}

.solution.hidden {
    display: none;
}

.solution h5 {
    color: #d97706;
    margin-bottom: 1rem;
}

.problem-navigation {
    display: flex;
    justify-content: space-between;
    gap: 1rem;
}

.problem-navigation button {
    padding: 0.75rem 1.5rem;
    border: 2px solid var(--primary-color);
    background: white;
    color: var(--primary-color);
    border-radius: 8px;
    cursor: pointer;
    font-weight: 500;
    transition: all 0.3s ease;
}

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

.problem-navigation button:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

/* Reference Styles */
.reference-container {
    max-width: 1000px;
    margin: 0 auto;
}

.reference-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 2rem;
    margin-bottom: 3rem;
}

.reference-card {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.reference-card h4 {
    color: var(--primary-color);
    margin-bottom: 1rem;
    font-size: 1.3rem;
}

.reference-card ul {
    list-style: none;
}

.reference-card li {
    margin-bottom: 0.75rem;
    padding-left: 1rem;
    position: relative;
}

.reference-card li::before {
    content: "•";
    color: var(--primary-color);
    position: absolute;
    left: 0;
    font-weight: bold;
}

.examples {
    background: var(--card-bg);
    padding: 2rem;
    border-radius: 12px;
    box-shadow: var(--shadow);
}

.examples h4 {
    color: var(--primary-color);
    margin-bottom: 1.5rem;
    font-size: 1.3rem;
}

.example {
    background: #f8fafc;
    padding: 1.5rem;
    border-radius: 8px;
    border: 1px solid var(--border-color);
}

.example strong {
    color: var(--primary-color);
}

.example ul {
    margin-top: 0.5rem;
    margin-left: 1rem;
}

/* Responsive Design */
@media (max-width: 768px) {
    .venn-container {
        grid-template-columns: 1fr;
    }
    
    .tab-btn {
        padding: 0.75rem 1rem;
        font-size: 0.9rem;
    }
    
    header h1 {
        font-size: 2rem;
    }
    
    .operation-buttons {
        grid-template-columns: 1fr;
    }
    
    .calc-operations {
        grid-template-columns: 1fr;
    }
    
    .difficulty-selector {
        flex-direction: column;
        align-items: center;
    }
    
    .reference-grid {
        grid-template-columns: 1fr;
    }
    
    .problem-navigation {
        flex-direction: column;
    }
}

/* Animation for smooth transitions */
.tab-content {
    animation: fadeIn 0.3s ease-in-out;
}

@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Venn diagram element styles */
.venn-element {
    font-size: 14px;
    font-weight: 500;
    cursor: pointer;
    transition: all 0.2s ease;
}

.venn-element:hover {
    font-size: 16px;
    font-weight: 600;
}

.highlight {
    fill: #fbbf24 !important;
    stroke: #d97706 !important;
    stroke-width: 2px !important;
}