JSFiddle - React, Tailwind, and code Playground

HTML

<div class="testdiv">
<!--put js code here -->
</div>
<div class="testdiv">do not put js here</div>
<div class="testdiv">do not put js here</div>
<div class="testdiv">do not put js here</div>
<div class="testdiv">do not put js here</div>
<div class="testdiv">do not put js here</div>

CSS

.testdiv{
  border:1px solid #585858;
   margin:5px;padding:5px;
}

JavaScript

var codeString ="aaa";

$('.testdiv:first').css({
    'border':'2px solid #ff0000',
});

$(codeString).appendTo('.testdiv');