:root {
    --primary: #2c3e50;
    --secondary: #e74c3c;
    --accent: #3498db;
    --light: #ecf0f1;
    --dark: #2c3e50;
    --success: #2ecc71;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    background-color: #f5f5f5;
    color: #333;
    line-height: 1.6;
}

.container {
    width: 90%;
    max-width: 1200px;
    margin: 0 auto;
    padding: 20px;
}

header {
    background-color: var(--primary);
    color: white;
    padding: 1rem 0;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

header h1 {
    text-align: center;
    margin-bottom: 10px;
}

nav {
    display: flex;
    justify-content: center;
    gap: 20px;
}

nav button {
    background: none;
    border: none;
    color: white;
    padding: 10px 15px;
    cursor: pointer;
    font-weight: bold;
    border-radius: 4px;
    transition: background-color 0.3s;
}

nav button:hover, nav button.active {
    background-color: rgba(255,255,255,0.1);
}

.section {
    display: none;
    padding: 20px;
    background: white;
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0,0,0,0.1);
    margin-top: 20px;
}

.section.active {
    display: block;
}

h2 {
    color: var(--primary);
    margin-bottom: 20px;
    padding-bottom: 10px;
    border-bottom: 2px solid var(--light);
}

.form-group {
    margin-bottom: 15px;
}

label {
    display: block;
    margin-bottom: 5px;
    font-weight: bold;
}

input, select, textarea {
    width: 100%;
    padding: 10px;
    border: 1px solid #ddd;
    border-radius: 4px;
    font-size: 16px;
}

button {
    background-color: var(--accent);
    color: white;
    border: none;
    padding: 12px 20px;
    border-radius: 4px;
    cursor: pointer;
    font-size: 16px;
    transition: background-color 0.3s;
}

button:hover {
    background-color: #2980b9;
}

.btn-delete {
    background-color: var(--secondary);
}

.btn-delete:hover {
    background-color: #c0392b;
}

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

.btn-success:hover {
    background-color: #27ae60;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 20px;
}

th, td {
    padding: 12px 15px;
    text-align: left;
    border-bottom: 1px solid #ddd;
}

th {
    background-color: var(--light);
    font-weight: bold;
}

tr:hover {
    background-color: #f9f9f9;
}

.alert {
    padding: 15px;
    margin-bottom: 20px;
    border-radius: 4px;
    display: none;
}

.alert-success {
    background-color: #d4edda;
    color: #155724;
    border: 1px solid #c3e6cb;
}

.alert-error {
    background-color: #f8d7da;
    color: #721c24;
    border: 1px solid #f5c6cb;
}

.exercise-set {
    display: flex;
    gap: 10px;
    margin-bottom: 10px;
    align-items: center;
}

.exercise-set input {
    flex: 1;
}

.add-set {
    margin-bottom: 15px;
}

.stats-container {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(300px, 1fr));
    gap: 20px;
}

.stat-card {
    background-color: var(--light);
    padding: 20px;
    border-radius: 8px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

.stat-card h4 {
    margin-bottom: 10px;
    color: var(--primary);
}

.stat-number {
    font-size: 2rem;
    font-weight: bold;
    color: var(--accent);
}

@media (max-width: 768px) {
    .container {
        width: 95%;
        padding: 10px;
    }
    
    .exercise-set {
        flex-direction: column;
    }
    
    .exercise-set input {
        width: 100%;
    }
    
    table {
        font-size: 14px;
    }
    
    th, td {
        padding: 8px 10px;
    }
    
    .stats-container {
        grid-template-columns: 1fr;
    }
}