JSFiddle - React, Tailwind, and code Playground

HTML

Klick mich: <input name="vorname" id="wasauchimmer" type="text">

JavaScript

var element = document.getElementById( 'wasauchimmer' );
element.onfocus = function(event) {
    element.style.backgroundColor='#00FF00'; //Grün
};
element.onblur = function(event) {
    element.style.backgroundColor='#0000FF'; //Blau
};