JSFiddle - React, Tailwind, and code Playground

HTML

<div class="myStyle" ><p>
blah blah
</p></div>

CSS

*,
*:before,
*:after {
    /*This comes from bootstrap*/
    background-color: red !important;
}
*,
*:before,
*:after {
  /*What can I put here to undo bootstrap so that my block is blue?*/
    background-color: initial !important;
}
.myStyle {
    background-color:blue;
}