html, body {
    height: 100%;
    margin: 0;
    padding: 0;
    background-color: black;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
}

div.centered {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100%;
    width: 66%;
    background-color: #303030;
    border-radius: 15px;
}

div.calculator {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(5, 1fr);
    gap: 5px;
    padding: 5px;
}

input.display {
    grid-column: 2 / span 3;
    font-family: "Orbitron", serif;
    color: white;
    background-color: #404040;
    border: 1px solid #808080;
    text-align: right;
    font-size: 120%;
}

button {
    padding-top: 0.6em;
    padding-bottom: 0.6em;
    border: 1px solid #808080;
    font-weight: bold;
    border-radius: 5px;
}

button.number {
    background-color: #606060;
    color: white;
}

button.operator {
    background-color: #404040;
    color: white;
}

button.calculate {
    background-color: #3355dd;
    color: white;
    grid-column: 4;
}