*{
    margin: 0;
    padding: 0;
        box-sizing: border-box;
    }
    
    body{
        min-height: 100vh;
        display: flex;
        align-items: center;
        justify-content: center;
    
    }
    
    .calculator{
        flex: 0 0 95%;
    }
    .screen{
        width: 100%;
        font-size: 7rem;
        padding: 0.5rem;
        background: rgb(41,41,56);
        color: white;
        border:none;
    }
    
    .buttons{
        display: flex;
        flex-wrap: wrap;
        transition: all 0.5s linear;
    }
    
    button{
        flex:0 0 25%;
        border: 1px solid black;
        padding: 0.25rem 0;
        transition: all 2s ease;
    }
    button:hover{
        background: blue;
    }
    .btn-yellow{
        background:grey;
        color: white;
    }
    .btn-grey{
        background: rgb(224,224,224);
    }
    .btn,.btn-equal,.btn-clear{
        font-size: 4rem;
    }
    .btn-equal{
        background: green;
    }
    .btn-clear{
        background: red;
    }