style.css

body{
    background-color: whitesmoke;
}
::placeholder{
    color: black;
}
.calc{
    width: 400px;
    height: 550px;
    margin:auto auto;
    padding: auto;
    background-color: darkgrey;
    border: 2px black ridge;
    border-radius: 7px;
    /*max-width: auto;
    max-height: auto;
    min-width: auto;             \\ By Jerin jj
    min-height: auto;*/
}
.screen{
    width: 95%;
    height: 90px;
    margin: 7px;
    border-radius: 6px;
    border: 1px white solid;
    text-align: right;
    font-size: 30px;
    pointer-events: none;
}
.btn{
    height: 50px;
    width: 80px;
    margin-left: 14px;
    margin-top: 30px;
    font-size: x-large;
    color: #fff;
    background: dimgray;
    border: 1px solid dimgray;
    border-radius: 4px;
}

.btn:active{
    height: 50px;
    width: 80px;
    margin-left: 14px;
    margin-top: 30px;
    font-size: x-large;
    text-shadow: 0px 0px 25px #fff;
    border: #fff 2px solid;
    border-radius: 4px;
}