JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text"  name="Msg" id="Msg" value="Bien inséré !" />

JavaScript

function changeC(){

      var Msg = document.getElementById ("Msg");  
      if (Msg.value=='Bien inséré !') {  
       Msg.style.border="2px solid #FF0000";
       Msg.style.backgroundColor= "#00FF00" ;
      }
    }  

changeC()