border color for input box in html code example
Example 1: add border to input css
border: none;
border-bottom: 1px solid blue;
Example 2: how to change input border color with js
document.getElementById("fName").className = document.getElementById("fName").className + " error"; // this adds the error class
document.getElementById("fName").className = document.getElementById("fName").className.replace(" error", ""); // this removes the error class