body {
    width: 45%;
}
/* Result Styling  */
#res {
    background-color: lightgray;
    border: solid;
    height: 48px;
    font-size: 20px;
}

/* Button Styling */
#btns {
    grid-template-columns: auto auto auto auto;
}

#btn0, #btn1 {
    background-color: lightgreen; 
    color: brown;
}

#btnClr, #btnEql {
    background-color: darkgreen; 
    color: white;
}

#btnSum, #btnSub, #btnMul, #btnDiv {
    background-color: black;
    color: red; 
}

#btns button {
    width: 25%;
    height: 36px;
    font-size: 18px;
    margin: 0px;
    float: left;
}

@media (max-width: 1300px) {
    body {
        width: 70%;
    }   
}

@media (max-width: 900px) {
    body {
        width: 100%;
    }   
}