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

:root {
    --primary-color: #2c3e50;
    --secondary-color: #34495e;
    --accent-color: #3498db;
    --success-color: #27ae60;
    --danger-color: #e74c3c;
    --light-bg: #ecf0f1;
    --white: #ffffff;
    --text-dark: #2c3e50;
    --text-light: #7f8c8d;
    --border-color: #bdc3c7;
    --shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 4px 8px rgba(0, 0, 0, 0.15);
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--light-bg);
    color: var(--text-dark);
    line-height: 1.6;
}

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

header {
    background-color: var(--primary-color);
    color: var(--white);
    padding: 30px;
    border-radius: 8px;
    margin-bottom: 30px;
    box-shadow: var(--shadow-lg);
}

header h1 {
    font-size: 2.5rem;
    margin-bottom: 8px;
}

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

main {
    display: flex;
    flex-direction: column;
    gap: 30px;
}

section {
    background-color: var(--white);
    padding: 30px;
    border-radius: 8px;
    box-shadow: var(--shadow);
}

section h2 {
    font-size: 1.8rem;
    margin-bottom: 20px;
    color: var(--primary-color);
    border-bottom: 2px solid var(--accent-color);
    padding-bottom: 10px;
}

.timer-display {
    font-size: 4rem;
    font-weight: bold;
    text-align: center;
    color: var(--accent-color);
    font-family: 'Courier New', monospace;
    margin: 30px 0;
    padding: 20px;
    background-color: var(--light-bg);
    border-radius: 8px;
}

.timer-controls {
    display: flex;
    justify-content: center;
    gap: 15px;
    flex-wrap: wrap;
}

.btn {
    padding: 12px 30px;
    font-size: 1rem;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    transition: all 0.3s ease;
    font-weight: 600;
}

.btn:hover:not(:disabled) {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.btn:active:not(:disabled) {
    transform: translateY(0);
}

.btn:disabled {
    opacity: 0.5;
    cursor: not-allowed;
}

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

.btn-primary:hover:not(:disabled) {
    background-color: #229954;
}

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

.btn-secondary:hover:not(:disabled) {
    background-color: #c0392b;
}

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

.btn-tertiary:hover:not(:disabled) {
    background-color: var(--primary-color);
}

.btn-large {
    width: 100%;
    padding: 15px;
    font-size: 1.1rem;
}

.btn-delete {
    background-color: var(--danger-color);
    color: var(--white);
    padding: 8px 16px;
    font-size: 0.9rem;
}

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

.form-group {
    margin-bottom: 20px;
}

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

.form-group input,
.form-group textarea {
    width: 100%;
    padding: 12px;
    border: 2px solid var(--border-color);
    border-radius: 5px;
    font-size: 1rem;
    font-family: inherit;
    transition: border-color 0.3s ease;
}

.form-group input:focus,
.form-group textarea:focus {
    outline: none;
    border-color: var(--accent-color);
}

.form-group input[readonly] {
    background-color: var(--light-bg);
    cursor: not-allowed;
}

.table-container {
    overflow-x: auto;
}

table {
    width: 100%;
    border-collapse: collapse;
    margin-top: 10px;
}

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

th {
    padding: 15px;
    text-align: left;
    font-weight: 600;
}

td {
    padding: 15px;
    border-bottom: 1px solid var(--border-color);
}

tbody tr:hover {
    background-color: var(--light-bg);
}

.no-entries td {
    text-align: center;
    color: var(--text-light);
    font-style: italic;
    padding: 40px;
}

footer {
    text-align: center;
    margin-top: 40px;
    padding: 20px;
    color: var(--text-light);
    font-size: 0.9rem;
}

@media (max-width: 768px) {
    header h1 {
        font-size: 2rem;
    }

    .timer-display {
        font-size: 3rem;
    }

    section {
        padding: 20px;
    }

    table {
        font-size: 0.9rem;
    }

    th, td {
        padding: 10px;
    }
}

@media (max-width: 480px) {
    .container {
        padding: 10px;
    }

    header h1 {
        font-size: 1.5rem;
    }

    .timer-display {
        font-size: 2.5rem;
    }

    .timer-controls {
        flex-direction: column;
    }

    .btn {
        width: 100%;
    }
}