html{
    font-size:62.5%;
    box-sizing:border-box;
}
 
*,*::before,*::after{
    margin:0;
    padding:0;
    box-sizing:inherit;
}

.calculator{
    border:1px solid #ccc;
    border-radius:5px;
    position:absolute;
    top:50%;
    left:50%;
    transform:translate(-50%, -50%);    
    width:400px;
}

.card {
    box-shadow: 0 2px 5px 0 rgb(0 0 0 / 16%), 0 2px 10px 0 rgb(0 0 0 / 12%);
    border: 0;
    font-weight: 400;
}

.calculator-screen{
    width:100%;
    height:80px;
    border:none;
    background-color:black;
    color:white;
    text-align:right;
    padding-right:20px;
    padding-left:20px;
    font-size:4em;
}

button{
    height:60px;
    font-size:2rem !important;
}

.equal-sign{
    height:98%;
    grid-area:2 / 4 / 6 / 5;
}

.calculator-keys{
    display:grid;
    grid-template-columns:repeat(4,1fr);
    grid-gap:20px;
    padding:20px;
}
.btn-default {
    background-color: #2bbbad!important;
    color: #fff;
}
.btn-info {
    color: #fff;
    
}
.waves-effect {
    position: relative;
    cursor: pointer;
    overflow: hidden;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
    -webkit-tap-highlight-color: transparent;
}

.btn-light {
    background-color: #e0e0e0!important;
    color: #000;
}
.equal-sign :hover{
    color:black;
}
.btn-default:hover{
    background-color:darkgreen;
}