how to add border color to form in html code example

Example: javascript for border color

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