style.css

*{
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
}
h1{
    margin-bottom: 50px;
    font-family: 'Courier New', Courier, monospace;
    text-align: center;
}
body{
    display: flex;
    justify-content: center;
    align-items: center;
    flex-direction: column;
    flex-wrap: wrap;
    min-height: 100vh;
    background: linear-gradient(45deg,lightBlue,violet);
    background: cover;
}
.calculator{
    display: grid;
    position: relative;
    box-shadow: 10px 10px 10px 10px black;
}

.calculator .value{
    grid-column: span 4;
    height: 100px;
    padding: 10px;
    background: gray;
    border: none;
    outline: none;
    font-size: 20px;
    text-align: right;
}
.calculator span{
    display: grid;
    width: 80px;
    height: 80px;
    background: #0c2835;
    place-items: center;
    color: white;
    font-size: 20px;
    border: 2px solid rgba(0, 0, 0, 0.1);
}
span:active{
    background-color: rgb(99, 205, 50);
    color: black;
}
.calculator span.clear{
    background: #ff3077;
}
.calculator span.plus{
    grid-row: span 2;
    height: 160px;
}
.calculator .equal{
    background: #03b1ff;
}