* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: sans-serif;
}

body {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: #000;
}

.calculator {
    background: #fff;
    padding: 20px;
    border-radius: 10px;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.1);
}

.display {
    text-align: right;
    margin-bottom: 20px;
}

.result {
    font-size: 36px;
    font-weight: bold;
    margin-bottom: 10px;
}

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

.num-btn, .op-btn, .dec-btn, .eq-btn, .clear-btn {
    padding: 10px;
    border: none;
    border-radius: 5px;
    outline: none;
    cursor: pointer;
    font-size: 24px;
}

.num-btn, .dec-btn {
    background: #fff;
}

.op-btn, .eq-btn {
    background: #007bff;
    color: #fff;
}

.clear-btn {
    background: #ff0000;
    color: #fff;
}