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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #121212;
    font-family: Arial, sans-serif;
}

.calculator {
    background: #1f1f1f;
    padding: 20px;
    border-radius: 10px;
    width: 300px;
}

#display {
    width: 100%;
    height: 50px;
    margin-bottom: 15px;
    font-size: 24px;
    text-align: right;
    padding: 10px;
    border-radius: 5px;
    border: none;

    background-color: #1a1a1a;  /* darker background */
    color: #ffffff;             /* bright white text */
}

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

button {
    padding: 15px;
    font-size: 18px;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    background-color: #e0e0e0;   /* Light grey */
    color: #111;                /* Dark text */
    transition: 0.2s;
}

button:hover {
    background-color: #cfcfcf;
}

.zero {
    grid-column: span 2;
}