:root {
    --bg-color: #f0f2f5;
    --card-bg: #ffffff;
    --text-color: #333;
    --accent-color: #007bff;
    --accent-hover: #0056b3;
    --stop-color: #dc3545;
    --stop-hover: #a71d2a;
}

body {
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: var(--bg-color);
    font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
    color: var(--text-color);
}

.container {
    background-color: var(--card-bg);
    padding: 3rem;
    border-radius: 20px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
    text-align: center;
    min-width: 320px;
}

.display {
    font-size: 5rem;
    font-weight: 700;
    font-family: 'Courier New', Courier, monospace;
    margin-bottom: 2rem;
    color: var(--text-color);
    letter-spacing: 2px;
}

.controls {
    display: flex;
    gap: 1rem;
    justify-content: center;
}

.btn {
    padding: 1rem 2rem;
    font-size: 1.2rem;
    font-weight: 600;
    cursor: pointer;
    border: none;
    border-radius: 50px;
    background-color: var(--accent-color);
    color: white;
    transition: all 0.2s ease;
    outline: none;
    box-shadow: 0 4px 15px rgba(0, 123, 255, 0.3);
    min-width: 120px;
}

.btn.secondary {
    background-color: #6c757d;
    box-shadow: 0 4px 15px rgba(108, 117, 125, 0.3);
}

.btn.secondary:hover:not(:disabled) {
    background-color: #5a6268;
    transform: translateY(-2px);
}

.btn:disabled {
    background-color: #ccc;
    box-shadow: none;
    cursor: not-allowed;
    transform: none;
}

.btn:hover {
    background-color: var(--accent-hover);
    transform: translateY(-2px);
    box-shadow: 0 6px 20px rgba(0, 123, 255, 0.4);
}

.btn:active {
    transform: translateY(0);
}

.btn.running {
    background-color: var(--stop-color);
    box-shadow: 0 4px 15px rgba(220, 53, 69, 0.3);
}

.btn.running:hover {
    background-color: var(--stop-hover);
    box-shadow: 0 6px 20px rgba(220, 53, 69, 0.4);
}