how to change input border color with js

1input:focus {
2	outline: none;
3  	border: 1px solid red;
4}

1 var getColor = prompt("Choose your color ", "Enter the  color ");
2 var color;
3 var el = document.getElementById("color");
4 el.innerHTML = "Whatever paragraph message.";
5 if (getColor =="Yellow" || getColor =="yellow" || getColor =="YELLOW"){
6     color = "#FFFF66";
7     el.style.borderColor = color;
8 }

1 
2.borders{
3    background-color:#00ffff;
4    border-color:#000000;
5    border-width:2px;
6    border-style:solid;
7}

1document.getElementById("fName").className = document.getElementById("fName").className + " error";  // this adds the error class
2
3document.getElementById("fName").className = document.getElementById("fName").className.replace(" error", ""); // this removes the error class
4