style.css

*{
    padding: 0;
    margin: 0;
    box-sizing: border-box;
    font-family: Arial, Helvetica, sans-serif;
}

body{
    height: 100vh;
    background: linear-gradient(to bottom, #8f2cff 50%, #090c31 50%);
}

.calculadora{
    width: 400px;
    background-color: #15173c;
    padding: 50px 30px;
    position: absolute;
    transform: translate(-50%, -50%);
    top: 50%;
    left: 50%;
    border-radius: 10px;
    box-shadow: 0 20px 50px rgba(0, 5, 24, 0.4);

}

.display{
    width: 100%;
}

.display input{
    width: 100%;
    padding: 15px 10px;
    text-align: right;
    border: none;
    background-color: transparent;
    color: #ffffff;
    font-size: 35px;
}

.display input::placeholder {
    color: #9490ac;
}

.buttons{
    margin-top: 40px;
    display: grid;
    grid-template-columns: repeat(4,1fr);
    grid-gap: 2px;
}

.buttons input[type="button"]{
    font-size: 20px;
    padding: 17px;
    border: none;
    background-color: transparent;
    color: #ffffff;
    cursor: pointer;
    border-radius: 5px;
}

.buttons input[type="button"]:hover{
    box-shadow: 0 8px 25px #000d2e;
}

input[type="button"]#equal {
    background-color: #8f2cff;
    grid-row: span 2;
}

input[type="button"][value="0"] {
    grid-column: span 2;
}