JSFiddle - React, Tailwind, and code Playground

HTML

<div id="d2" style = "text-decoration: underline; border-radius: 5px 5px 5px 5px;">HELLO - my style is "text-decoration: underline; border-radius: 5px;"</div>

<hr>
<div id="result"></div>

JavaScript

function outerHTML(node){
  return node.outerHTML || new XMLSerializer().serializeToString(node);
}
function trimString(s) {
  var l = 0, r = s.length - 1;  
  while(l < s.length && s[l] == ' ') l++;  
  while(r > l && s[r] == ' ') r -= 1;  
  return s.substring(l, r + 1);
}
function getStyleAsInHTML(node) {
  var parts, part, sIndex = -1, i, style = '', delim;
  parts = outerHTML(node);
  parts = parts.replace(/\s/g," ");
  parts = parts.split('=');
  
  for(i=0; i<parts.length; i++) {
    part = trimString(parts[i]);
    if(part.length >= 5 && part.substring(part.length-5).toLowerCase()=='style') {
      sIndex = i+1;
      break;
    }
  }
  if(sIndex!=-1 && sIndex<parts.length) {
    style = parts[sIndex];
    delim = style.charAt(0);
    for(i=style.length-1; i>0; i--) {
      if(style.charAt(i)==delim) {
        style = style.substring(1, i);
        break;
      }
    }
  }
  return style;
}
document.getElementById('result').innerHTML = 'Style as in HTML [' + getStyleAsInHTML(document.getElementById('d2')) + ']';