JSFiddle - React, Tailwind, and code Playground

HTML

<div id="todolist">
      
     <input class="addtodo" placeholder="New todo task" name="TITLE"  type="text" />
     <span class="add-on">OK</span>
 </div>

CSS

#post-todo span{   
   color:#aaa;
 }

.addtodo:focus + .add-on
{
    background-color:yellow;
   color:blue;
}
.addtodo
{
    //color:red;
}