fist.css

*{
    margin: 0;
    padding: 0;
    font-family: sans-serif;
    box-sizing: border-box;
}
body{
    width: 100%;
    width: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #3a443a;
}
.calculator{
    border: 2px solid black;
    padding: 20px;
    border-radius: 15px;
    background: transparent;
    box-shadow: 0px 3px 15px rgba(113,115,119,0.5);
}
input{
    width: 320px;
 border: none;
 padding: 24px;
 background: transparent;
 box-shadow: 0px 3px 15px rgba(84,84,84,0.1);
 font-size: 40px;
 text-align: right;
 cursor: pointer;
 color: #ffff;
}
input::placeholder{
color: #ffff;
}
button{
    width: 60px;
    border: none;
    height: 60px;
    margin: 10px;
    border-radius: 50%;
    background: transparent;
    color: #ffff;
    font-size: 20px;
    box-shadow: -8px -8px 15px rgba(255,255,255,0.3);
    cursor: pointer;
}
.equalBtn{
    background-color: orange;
}
.mul{
    color: rgb(10, 241, 10);
}