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

:root {
    --primary: #e74c3c;
    --primary-dark: #c0392b;
    --secondary: #a61e1e;
    --accent: #ef4444;
    --text: #1f2937;
    --text-light: #6b7280;
    --background: #ffffff;
    --background-alt: #fef2f2;
    --border: #fecaca;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1);
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    line-height: 1.7;
    color: var(--text);
    background: var(--background-alt);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 20px;
}

/* Header */
.main-header {
    background: linear-gradient(135deg, #e74c3c 0%, #000000 100%);
    color: white;
    padding: 80px 0 60px;
    text-align: center;
    position: relative;
    overflow: hidden;
}

.main-header::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: url('data:image/svg+xml,<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 1000 100" fill="rgba(255,255,255,0.1)"><polygon points="1000,100 1000,0 0,100"/></svg>');
    background-size: cover;
}

.header-content {
    position: relative;
    z-index: 2;
}

.main-header h1 {
    font-size: 3.5rem;
    font-weight: 800;
    margin-bottom: 20px;
    letter-spacing: -0.02em;
}

.main-header .subtitle {
    font-size: 1.3rem;
    opacity: 0.9;
    font-weight: 400;
    max-width: 600px;
    margin: 0 auto 30px;
}

/* Calculator Section */
.calculator-section {
    margin: -40px auto 60px;
    position: relative;
    z-index: 10;
}

.calculator-card {
    background: var(--background);
    border-radius: 20px;
    box-shadow: var(--shadow-lg);
    padding: 40px;
    margin-bottom: 40px;
}

.calculator-header {
    text-align: center;
    margin-bottom: 40px;
}

.calculator-header h2 {
    font-size: 2.2rem;
    font-weight: 700;
    color: var(--text);
    margin-bottom: 10px;
}

.calculator-header p {
    color: var(--text-light);
    font-size: 1.1rem;
}

.calculator-tabs {
    display: flex;
    gap: 10px;
    margin-bottom: 30px;
    flex-wrap: wrap;
}

.tab-btn {
    padding: 12px 24px;
    background: var(--background-alt);
    border: 2px solid var(--border);
    border-radius: 12px;
    font-weight: 600;
    color: var(--text-light);
    cursor: pointer;
    transition: all 0.3s ease;
    flex: 1;
    min-width: 120px;
    text-align: center;
}

.tab-btn.active {
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    color: white;
    border-color: var(--primary);
}

.tab-btn:hover:not(.active) {
    border-color: var(--primary);
    color: var(--primary);
}

.calculator-content {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 40px;
    align-items: start;
}

@media (max-width: 768px) {
    .calculator-content {
        grid-template-columns: 1fr;
    }
}

.input-section {
    background: var(--background-alt);
    padding: 30px;
    border-radius: 16px;
    border: 2px dashed var(--border);
}

.input-group {
    margin-bottom: 25px;
}

.input-group label {
    display: block;
    margin-bottom: 8px;
    font-weight: 600;
    color: var(--text);
}

.input-with-icon {
    position: relative;
}

.input-with-icon input, .input-with-icon select {
    width: 100%;
    padding: 15px 45px 15px 15px;
    border: 2px solid var(--border);
    border-radius: 12px;
    font-size: 1.1rem;
    transition: all 0.3s ease;
    background: var(--background);
}

.input-with-icon input:focus, .input-with-icon select:focus {
    outline: none;
    border-color: var(--primary);
    box-shadow: 0 0 0 3px rgba(231, 76, 60, 0.1);
}

.input-icon {
    position: absolute;
    right: 15px;
    top: 50%;
    transform: translateY(-50%);
    color: var(--text-light);
}

.select-group {
    margin-top: 5px;
}

.select-group select {
    width: 100%;
    padding: 8px;
    border: 1px solid var(--border);
    border-radius: 5px;
    background: var(--background);
}

.calculate-btn {
    width: 100%;
    padding: 16px;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    color: white;
    border: none;
    border-radius: 12px;
    font-size: 1.1rem;
    font-weight: 700;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 10px;
}

.calculate-btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 8px 25px rgba(231, 76, 60, 0.3);
}

.result-section {
    background: linear-gradient(135deg, #fef2f2 0%, #fee2e2 100%);
    padding: 30px;
    border-radius: 16px;
    border: 2px solid #fecaca;
}

.result-header {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-bottom: 20px;
}

.result-header i {
    color: var(--accent);
    font-size: 1.5rem;
}

.result-header h3 {
    font-size: 1.3rem;
    color: var(--text);
}

.result-value {
    font-size: 2.5rem;
    font-weight: 800;
    color: var(--primary);
    text-align: center;
    margin: 20px 0;
}

.result-details {
    background: white;
    padding: 20px;
    border-radius: 12px;
    border-left: 4px solid var(--accent);
}

.result-details p {
    margin-bottom: 8px;
    color: var(--text);
}

.formula-display {
    background: var(--background);
    padding: 15px;
    border-radius: 8px;
    font-family: 'Monaco', 'Consolas', monospace;
    font-size: 0.9rem;
    color: var(--text);
    border: 1px solid var(--border);
    margin-top: 15px;
}

/* Content Section */
.content-section {
    background: var(--background);
    border-radius: 20px;
    box-shadow: var(--shadow);
    padding: 50px;
    margin-bottom: 40px;
}

.content-section h2 {
    font-size: 2.5rem;
    font-weight: 700;
    color: var(--text);
    margin-bottom: 30px;
    position: relative;
}

.content-section h2::after {
    content: '';
    position: absolute;
    bottom: -10px;
    left: 0;
    width: 60px;
    height: 4px;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    border-radius: 2px;
}

.content-section h3 {
    font-size: 1.8rem;
    font-weight: 600;
    color: var(--text);
    margin: 40px 0 20px;
}

.content-section p {
    margin-bottom: 20px;
    color: var(--text);
    font-size: 1.1rem;
}

.highlight-box {
    background: linear-gradient(135deg, #fef2f2 0%, #fee2e2 100%);
    border-left: 4px solid var(--primary);
    padding: 25px;
    border-radius: 0 12px 12px 0;
    margin: 25px 0;
}

.highlight-box h4 {
    color: var(--primary);
    margin-bottom: 10px;
    font-size: 1.2rem;
}

.formula-box {
    background: var(--background);
    border: 2px solid var(--border);
    border-radius: 12px;
    padding: 25px;
    margin: 25px 0;
    position: relative;
}

.formula-box h4 {
    color: var(--primary);
    margin-bottom: 15px;
    font-size: 1.1rem;
}

.formula {
    font-family: 'Monaco', 'Consolas', monospace;
    font-size: 1.2rem;
    background: var(--background-alt);
    padding: 15px;
    border-radius: 8px;
    text-align: center;
    margin: 15px 0;
    border: 1px dashed var(--border);
}

.example-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
    gap: 25px;
    margin: 30px 0;
}

.example-card {
    background: var(--background);
    border: 2px solid var(--border);
    border-radius: 12px;
    padding: 25px;
    transition: all 0.3s ease;
}

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

.example-card h5 {
    color: var(--primary);
    margin-bottom: 15px;
    font-size: 1.1rem;
}

/* BMI Categories */
.bmi-categories {
    margin: 30px 0;
}

.category-grid {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
    gap: 15px;
    margin-top: 15px;
}

.category-item {
    padding: 15px;
    border-radius: 5px;
    text-align: center;
    color: white;
    font-weight: bold;
}

.underweight {
    background-color: #3498db;
}

.normal {
    background-color: #2ecc71;
}

.overweight {
    background-color: #f39c12;
}

.obese {
    background-color: #e74c3c;
}

/* Table Styles */
.table-container {
    overflow-x: auto;
    margin-top: 15px;
}

table {
    width: 100%;
    border-collapse: collapse;
}

th, td {
    padding: 10px;
    text-align: left;
    border-bottom: 1px solid var(--border);
}

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

/* More Calculators */
.more-calculators {
    text-align: center;
    padding: 60px 0;
}

.more-calculators h2 {
    font-size: 2.2rem;
    margin-bottom: 20px;
    color: var(--text);
}

.more-calculators p {
    color: var(--text-light);
    margin-bottom: 40px;
    font-size: 1.1rem;
}

.cta-button {
    display: inline-flex;
    align-items: center;
    gap: 12px;
    padding: 18px 36px;
    background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
    color: white;
    text-decoration: none;
    border-radius: 12px;
    font-weight: 700;
    font-size: 1.1rem;
    transition: all 0.3s ease;
}

.cta-button:hover {
    transform: translateY(-3px);
    box-shadow: 0 12px 30px rgba(231, 76, 60, 0.3);
}

/* Footer */
.main-footer {
    background: linear-gradient(135deg, #000000 0%, #333333 100%);
    color: white;
    text-align: center;
    padding: 40px 0;
    margin-top: 60px;
}

@media (max-width: 768px) {
    .main-header h1 {
        font-size: 2.5rem;
    }
    
    .calculator-card {
        padding: 25px;
    }
    
    .content-section {
        padding: 30px;
    }
    
    .tab-btn {
        flex: 1 1 calc(50% - 10px);
        min-width: 140px;
    }
}

@media (max-width: 480px) {
    .main-header h1 {
        font-size: 2rem;
    }
    
    .container {
        padding: 0 15px;
    }
    
    .calculator-tabs {
        flex-direction: column;
    }
}

/* Tab Content Styles */
.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
    animation: fadeIn 0.5s ease;
}

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