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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    padding: 20px;
}

.container {
    background: white;
    border-radius: 20px;
    padding: 40px;
    box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
    max-width: 500px;
    width: 100%;
}

h1 {
    color: #333;
    margin-bottom: 30px;
    font-size: 28px;
    text-align: center;
}

.timer-config {
    background: #f8f9fa;
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 30px;
}

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

.input-group:last-child {
    margin-bottom: 0;
}

label {
    display: block;
    margin-bottom: 8px;
    color: #555;
    font-weight: 600;
    font-size: 14px;
}

input[type="number"] {
    width: 100%;
    padding: 12px;
    border: 2px solid #e0e0e0;
    border-radius: 8px;
    font-size: 16px;
    transition: border-color 0.3s;
}

input[type="number"]:focus {
    outline: none;
    border-color: #667eea;
}

.checkbox-group {
    display: flex;
    align-items: center;
    gap: 10px;
    margin-top: 20px;
    padding: 12px;
    background: white;
    border-radius: 8px;
}

.checkbox-group input[type="checkbox"] {
    width: 20px;
    height: 20px;
    cursor: pointer;
}

.checkbox-group label {
    margin: 0;
    cursor: pointer;
    font-weight: 500;
}

.timer-display {
    text-align: center;
    margin: 30px 0;
}

#timerDisplay {
    font-size: 56px;
    font-weight: bold;
    color: #667eea;
    letter-spacing: 4px;
    margin-bottom: 10px;
    font-variant-numeric: tabular-nums;
    transition: color 0.3s ease;
}

#timerDisplay.running {
    animation: pulse 2s ease-in-out infinite;
}

@keyframes pulse {
    0%, 100% {
        opacity: 1;
    }
    50% {
        opacity: 0.8;
    }
}

#intervalStatus {
    font-size: 20px;
    color: #666;
    font-weight: 500;
    padding: 10px;
    background: #f0f0f0;
    border-radius: 8px;
    display: inline-block;
}

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

button {
    flex: 1;
    padding: 15px 30px;
    font-size: 18px;
    font-weight: 600;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.3s;
    text-transform: uppercase;
    letter-spacing: 1px;
}

button:hover {
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
}

button:active {
    transform: translateY(0);
}

#startButton {
    background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    color: white;
}

#startButton:hover {
    background: linear-gradient(135deg, #5568d3 0%, #65408b 100%);
}

#stopButton {
    background: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    color: white;
}

#stopButton:hover {
    background: linear-gradient(135deg, #df82ea 0%, #e4465b 100%);
}

#resetButton {
    background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    color: white;
}

#resetButton:hover {
    background: linear-gradient(135deg, #3e9bed 0%, #00e1ed 100%);
}

.footer {
    text-align: center;
    margin-top: 20px;
    padding-top: 20px;
    border-top: 1px solid #e0e0e0;
    color: #888;
    font-size: 12px;
}

/* Responsive Design */
@media (max-width: 600px) {
    .container {
        padding: 20px;
    }

    h1 {
        font-size: 24px;
    }

    #timerDisplay {
        font-size: 42px;
    }

    #intervalStatus {
        font-size: 16px;
    }

    button {
        padding: 12px 20px;
        font-size: 16px;
    }

    .controls {
        flex-direction: column;
    }
}