body {
    background: #f5f5f5;
    display: flex;
    height: 100vh;
    align-items: center;
    justify-content: center;
    font-family: Arial, Helvetica, sans-serif;
}

.kalkulator {
    background: #222;
    padding: 20px;
    border-radius: 16px;
    box-shadow: 0 4px 24px rgba(0,0,0,0.2);
    width: 320px;
}

.display {
    width: 100%;
    height: 50px;
    font-size: 2em;
    text-align: right;
    margin-bottom: 18px;
    border: none;
    background: #333;
    color: #fff;
    border-radius: 8px;
    padding: 0 10px;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

.btn {
    padding: 18px 0;
    font-size: 1.2em;
    border: none;
    border-radius: 8px;
    background: #eee;
    color: #222;
    cursor: pointer;
    transition: background 0.2s;
}

.btn:active {
    background: #ccc;
}

.operator {
    background: #ff9800;
    color: #fff;
}

.operator:active {
    background: #e68900;
}

.equals {
    grid-column: span 4;
    background: #4caf50;
    color: #fff;
}

.equals:active {
    background: #388e3c;
}

#clear {
    background: #f44336;
    color: #fff;
}

#clear:active {
    background: #c62828;
}