:root {
    --primary-blue: #2196F3;
    --success-green: #4CAF50;
    --warning-amber: #FFC107;
    --error-red: #F44336;
    --accent-purple: #9C27B0;
    --bg-light: #f8f9fa;
    --bg-white: #ffffff;
    --text-dark: #333333;
    --text-light: #666666;
    --border-light: #e0e0e0;
    --shadow-light: 0 2px 10px rgba(0,0,0,0.1);
    --shadow-medium: 0 4px 20px rgba(0,0,0,0.15);
    --border-radius: 12px;
    --transition: all 0.3s ease;
}

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

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background-color: var(--bg-light);
    color: var(--text-dark);
    line-height: 1.6;
    padding-bottom: 80px;
}

.app-header {
    background: linear-gradient(135deg, var(--primary-blue), var(--accent-purple));
    color: white;
    padding: 1rem 0;
    box-shadow: var(--shadow-medium);
    position: sticky;
    top: 0;
    z-index: 100;
}

.header-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 0 1rem;
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.header-content h1 {
    font-size: 1.5rem;
    font-weight: 700;
}

.language-toggle {
    background: rgba(255,255,255,0.2);
    border: 1px solid rgba(255,255,255,0.3);
    color: white;
    padding: 0.5rem 1rem;
    border-radius: 25px;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.language-toggle:hover {
    background: rgba(255,255,255,0.3);
    transform: translateY(-2px);
}

.main-content {
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem 1rem;
}

.section {
    display: none;
    animation: fadeIn 0.5s ease-in-out;
}

.section.active {
    display: block;
}

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

.welcome-card, .calculator-card {
    background: var(--bg-white);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow-light);
    margin-bottom: 2rem;
}

.welcome-card h2, .calculator-card h2 {
    color: var(--primary-blue);
    margin-bottom: 1rem;
    font-size: 1.5rem;
}

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

.stat-card {
    background: linear-gradient(135deg, var(--success-green), var(--primary-blue));
    color: white;
    padding: 1.5rem;
    border-radius: var(--border-radius);
    text-align: center;
    box-shadow: var(--shadow-light);
    transition: var(--transition);
}

.stat-card:hover {
    transform: translateY(-5px);
    box-shadow: var(--shadow-medium);
}

.stat-card i {
    font-size: 2rem;
    margin-bottom: 0.5rem;
    opacity: 0.8;
}

.stat-card h3 {
    font-size: 1.5rem;
    font-weight: 700;
    margin-bottom: 0.25rem;
}

.stat-card p {
    opacity: 0.9;
    font-size: 0.9rem;
}

.calculator-form {
    display: grid;
    gap: 1rem;
    margin-bottom: 2rem;
}

.form-group {
    display: flex;
    flex-direction: column;
}

.form-group label {
    font-weight: 600;
    margin-bottom: 0.5rem;
    color: var(--text-dark);
}

.form-group input {
    padding: 0.75rem;
    border: 2px solid var(--border-light);
    border-radius: var(--border-radius);
    font-size: 1rem;
    transition: var(--transition);
}

.form-group input:focus {
    outline: none;
    border-color: var(--primary-blue);
    box-shadow: 0 0 0 3px rgba(33, 150, 243, 0.1);
}

.btn {
    padding: 0.75rem 1.5rem;
    border: none;
    border-radius: var(--border-radius);
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    text-decoration: none;
}

.btn-primary {
    background: linear-gradient(135deg, var(--primary-blue), var(--accent-purple));
    color: white;
}

.btn-primary:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-medium);
}

.results-section {
    background: var(--bg-light);
    padding: 1.5rem;
    border-radius: var(--border-radius);
    margin-top: 2rem;
}

.results-section.hidden {
    display: none;
}

.results-section h3 {
    color: var(--success-green);
    margin-bottom: 1rem;
}

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

.result-item {
    background: white;
    padding: 1rem;
    border-radius: var(--border-radius);
    box-shadow: var(--shadow-light);
    display: flex;
    justify-content: space-between;
    align-items: center;
}

.result-item strong {
    color: var(--success-green);
    font-size: 1.1rem;
}

.chart-canvas {
    width: 100%;
    height: 300px;
    border-radius: var(--border-radius);
    background: white;
    box-shadow: var(--shadow-light);
}

.faq-container {
    background: var(--bg-white);
    border-radius: var(--border-radius);
    padding: 2rem;
    box-shadow: var(--shadow-light);
}

.faq-container h2 {
    color: var(--primary-blue);
    margin-bottom: 2rem;
    text-align: center;
}

.faq-item {
    border-bottom: 1px solid var(--border-light);
    margin-bottom: 1rem;
}

.faq-question {
    width: 100%;
    background: none;
    border: none;
    padding: 1rem 0;
    text-align: left;
    font-size: 1.1rem;
    font-weight: 600;
    cursor: pointer;
    display: flex;
    justify-content: space-between;
    align-items: center;
    color: var(--text-dark);
    transition: var(--transition);
}

.faq-question:hover {
    color: var(--primary-blue);
}

.faq-icon {
    font-size: 1.2rem;
    transition: var(--transition);
}

.faq-question[aria-expanded="true"] .faq-icon {
    transform: rotate(45deg);
}

.faq-answer {
    padding: 0 0 1rem 0;
    color: var(--text-light);
    line-height: 1.6;
    overflow: hidden;
    transition: var(--transition);
}

.faq-answer[hidden] {
    display: none;
}

.bottom-nav {
    position: fixed;
    bottom: 0;
    left: 0;
    right: 0;
    background: var(--bg-white);
    border-top: 1px solid var(--border-light);
    display: flex;
    justify-content: space-around;
    padding: 0.5rem 0;
    box-shadow: 0 -2px 10px rgba(0,0,0,0.1);
    z-index: 100;
}

.nav-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    text-decoration: none;
    color: var(--text-light);
    padding: 0.5rem;
    border-radius: var(--border-radius);
    transition: var(--transition);
    min-width: 60px;
}

.nav-item i {
    font-size: 1.2rem;
    margin-bottom: 0.25rem;
}

.nav-item span {
    font-size: 0.75rem;
    font-weight: 500;
}

.nav-item.active {
    color: var(--primary-blue);
    background: rgba(33, 150, 243, 0.1);
}

.nav-item:hover {
    color: var(--primary-blue);
    transform: translateY(-2px);
}

footer {
    background: var(--text-dark);
    color: white;
    text-align: center;
    padding: 1rem;
    margin-top: 2rem;
}

footer p {
    font-size: 0.9rem;
    opacity: 0.8;
}

footer a {
    color: var(--primary-blue);
    text-decoration: none;
    transition: var(--transition);
}

footer a:hover {
    color: #1976D2;
    text-decoration: underline;
}

@media (max-width: 768px) {
    .main-content {
        padding: 1rem 0.5rem;
    }
    
    .welcome-card, .calculator-card {
        padding: 1.5rem;
    }
    
    .quick-stats {
        grid-template-columns: 1fr;
    }
    
    .result-grid {
        grid-template-columns: 1fr;
    }
    
    .result-item {
        flex-direction: column;
        text-align: center;
        gap: 0.5rem;
    }
    
    .header-content h1 {
        font-size: 1.25rem;
    }
    
    .chart-canvas {
        height: 250px;
    }
}

@media (max-width: 480px) {
    .nav-item span {
        font-size: 0.7rem;
    }
    
    .nav-item i {
        font-size: 1rem;
    }
    
    .faq-question {
        font-size: 1rem;
    }
    
    .form-group input {
        padding: 0.6rem;
    }
}

.loading {
    display: inline-block;
    width: 20px;
    height: 20px;
    border: 3px solid rgba(255,255,255,.3);
    border-radius: 50%;
    border-top-color: #fff;
    animation: spin 1s ease-in-out infinite;
}

@keyframes spin {
    to { transform: rotate(360deg); }
}

.error-message {
    background: var(--error-red);
    color: white;
    padding: 1rem;
    border-radius: var(--border-radius);
    margin: 1rem 0;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.success-message {
    background: var(--success-green);
    color: white;
    padding: 1rem;
    border-radius: var(--border-radius);
    margin: 1rem 0;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.pulse {
    animation: pulse 2s infinite;
}

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