body {
    background-color: #2c3e50;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

.calculator {
    background-color: #1c1c1c;
    padding: 20px;
    border-radius: 20px;
    box-shadow: 0px 10px 30px rgba(0,0,0,0.5);
    width: 320px;
}

#display {
    width: 100%;
    height: 60px;
    font-size: 24px;
    text-align: right;
    margin-bottom: 20px;
    padding: 10px;
    box-sizing: border-box;
    border: none;
    background: #333;
    color: #00ff00;
    border-radius: 10px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.btn {
    padding: 15px;
    font-size: 18px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background-color: #444;
    color: white;
    transition: 0.2s;
}

.btn:hover {
    background-color: #666;
}

.op {
    background-color: #f39c12;
    font-weight: bold;
}

.op:hover {
    background-color: #e67e22;
}

.sci {
    background-color: #34495e;
    font-size: 16px;
}

.ctrl {
    background-color: #e74c3c;
}

.equal {
    background-color: #27ae60;
    grid-column: span 1;
}