body {
    width: 100%; 
    background-color: burlywood;
    text-align: center;
    

}
.section{
    width: 100%;
    text-align: center;
    margin-left: 50%;  
}

h1{
   color: blue; 
   overflow: hidden;
   display: inline;
   margin-bottom: 30px;
   text-decoration: underline; 



}
  
#res {
    display: block;
    font-size: 20px;
    height: 48px;
    background-color: lightgray;
    border: 2px solid black;
    box-sizing: border-box;
    width: 90%;
    overflow: hidden;
    margin-left: 5%;
}
#btns {
    display: block;
    overflow: hidden;
    width: 90%;
    text-align: center;
    margin-left: 5%;
    padding: 0px;
    margin-right: 3%;
    
}
#btns button {
    display: block;
    float: left;
    width: 25%;
    height: 36px;
    font-size: 18px;
    background: black;
    color: red;
}
#btns #btn0, #btns #btn1 {
    background-color: lightgreen;
    color: brown;
}
#btns #btnClr, #btns #btnEql {
    background-color: darkgreen;
    color: white;
}