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

body {
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
    line-height: 1.6;
    color: #333;
    background-color: #f8f9fa;
}

.container {
    max-width: 800px;
    margin: 2rem auto;
    padding: 2rem;
    background-color: white;
    border-radius: 8px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

h1 {
    text-align: center;
    margin-bottom: 2rem;
    color: #2c3e50;
}

.tabs {
    display: flex;
    gap: 1rem;
    margin-bottom: 2rem;
    border-bottom: 1px solid #dee2e6;
    padding-bottom: 1rem;
}

.tab-btn {
    padding: 0.5rem 1rem;
    border: none;
    background: none;
    cursor: pointer;
    font-size: 1rem;
    color: #6c757d;
    transition: color 0.3s ease;
}

.tab-btn:hover {
    color: #2c3e50;
}

.tab-btn.active {
    color: #2c3e50;
    border-bottom: 2px solid #2c3e50;
}

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

label {
    display: block;
    margin-bottom: 0.5rem;
    font-weight: 500;
    color: #495057;
}

input, select {
    width: 100%;
    padding: 0.5rem;
    font-size: 1rem;
    border: 1px solid #ced4da;
    border-radius: 4px;
    transition: border-color 0.3s ease;
}

input:focus, select:focus {
    outline: none;
    border-color: #2c3e50;
    box-shadow: 0 0 0 2px rgba(44, 62, 80, 0.1);
}

#results {
    margin-top: 2rem;
    padding: 1.5rem;
    background-color: #f8f9fa;
    border-radius: 4px;
    opacity: 0;
    transform: translateY(10px);
    transition: all 0.3s ease;
}

#results.visible {
    opacity: 1;
    transform: translateY(0);
}

.hidden {
    display: none;
}

.result-text {
    font-size: 1.2em;
    margin: 1rem 0;
    line-height: 1.6;
}

.result-text strong {
    font-size: 1.4em;
    font-weight: bold;
    color: #2c3e50;
}

.reference-section {
    margin-top: 2rem;
    padding-top: 1rem;
    border-top: 1px solid #dee2e6;
}

.table-container {
    margin: 1rem 0;
    overflow-x: auto;
}

.reference-table {
    width: 100%;
    border-collapse: collapse;
    margin: 1rem 0;
    font-size: 0.9em;
}

.reference-table th,
.reference-table td {
    padding: 8px;
    text-align: center;
    border: 1px solid #dee2e6;
}

.reference-table th {
    background-color: #f8f9fa;
    font-weight: 600;
}

.reference-table tr.user-age {
    font-weight: bold;
}

.above-vo2max {
    background-color: #90EE90;
}

.below-vo2max {
    background-color: #FFB6C6;
}

.table-note {
    font-size: 0.9em;
    color: #666;
    margin-top: 1rem;
    font-style: italic;
}

/* Footer styles */
.footer {
    text-align: center;
    padding: 1rem 0;
    margin-top: 2rem;
    background-color: #f8f9fa;
    border-top: 1px solid #dee2e6;
}

.footer-content {
    font-size: 1.2em;
    color: #2c3e50;
}

.footer-link {
    text-decoration: none;
    color: #007bff;
    transition: color 0.3s ease;
}

.footer-link:hover {
    color: #0056b3;
}