body {
    background-color: #f7f7f7;
    font-family: sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.title {
    text-align: center;
    font-size: 20px;
    margin: 10px auto;
}

.calculator {
    background-color: #fff;
    border-radius: 4px;
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
    width: 375px;
    overflow: hidden;
}

.keys {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 5px;
    padding: 10px;
}

.keys button {
    background-color: #fff;
    border: 1px solid #e0e0e0;
    font-size: 2em;
    width: 100%;
    height: 70px;
    color: #444;
}

.display {
    background-color: #444;
    color: #fff;
    text-align: right;
    padding: 20px;
    font-size: 1.5em;
    height: 70px;
}

.keys button.is-depressed {
    background-color: #ccc;
    box-shadow: inset 0 0 3px #999;
}

.operator {
    background-color: #fa8231;
    color: #fff;
}

.clear,
.decimal {
    background-color: #888;
    color: #fff;
}

.clear {
    background-color: #f44336;
}