stylesheet.css

.calculator {
    text-align: center;
    margin: 0 auto;
    padding-top: 50px;
    width: 400px;
    border-radius: 20px;
}

.card {
    box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2);
    border-radius: 5px;
    padding: 30px;
    margin-top: 20px;
}

.calculator-screen {
    width: 100%;
    height: 100px;
    background-color: #252525;
    color: #555;
    text-align: center;
    font-size: 40px;
    border: none;
    padding: 0 20px;
    box-sizing: border-box;
}

.calculator-keys {
    width: 100%;
}

.row {
    display: flex;
}

button {
    height: 80px;
    background-color: #C9D8B6;
    border: 1px solid black;
    font-size: 32px;
    color: #fff;
    width: 25%;
    outline: none;
}

.all-clear,
.zero-btn {
    width: 50%;
}

.operator,
.equal-sign {
    background-color: #57837B;
}

button:hover {
    background-color: #b2c29e;
    font-weight: bold;
}

.operator:hover {
    background-color: #4b7a72;
}

.equal-sign:hover {
    background-color: #4b7a72;
}