Get stylesheets

HTML

<div class="row el">
  <p>
    Yupy yay yay!
  </p>
  <div class="el">
    yay 2
  </div>
</div>

CSS

.table tbody tr:hover th{ color: #fff; background: red; height: 300px;}

.el {
    background: black;
    color: #fff;
    height: 300px;
}

JavaScript

var stylesheets = document.styleSheets,
    stylesheet, new_stylesheet, rules, rule, i = 0,
    max_i = stylesheets.length,
    j, max_j;

for (i = max_i; i--;) {
    stylesheet = stylesheets[i];
    rules = stylesheet.cssRules;
    j = 0;
    max_j = rules.length;

    for (j = max_j; j--;) {
        rule = rules[j];
        if (rule && rule.selectorText.indexOf('.table tbody tr:hover th') > -1) {
            new_stylesheet = document.createElement('style');
            new_stylesheet.innerText = ".el:hover{" + rule.style.cssText + "}";
            document.getElementsByTagName('head')[0].appendChild(new_stylesheet);
        }
    }
}