JSFiddle - React, Tailwind, and code Playground

HTML

<div id="test">
    
</div>

CSS

#test{
    border-right-color: #000;
    
}

JavaScript

if(rgb2hex($("#test").css("border-right-color")) == "#000000"){
   console.log("yup");
   }

function rgb2hex(rgb){
 rgb = rgb.match(/^rgb\((\d+),\s*(\d+),\s*(\d+)\)$/);
 return "#" +
  ("0" + parseInt(rgb[1],10).toString(16)).slice(-2) +
  ("0" + parseInt(rgb[2],10).toString(16)).slice(-2) +
  ("0" + parseInt(rgb[3],10).toString(16)).slice(-2);
}