Highlighter selected text (based on https://jsfiddle.net/jsp04pd3/; also http://codepen.io/telekosmos/pen/PPQxQQ)

highlight.css

.highlight {
  background-color: yellow;
}

highlight.html

<div id="test">
    Select any part of <b>this text and</b> then click 'Run'.
</div>
<div id="test2">
    Select any part of <b>this text and</b> then click 'Run'.
</div>

<button id="execute">Run</button>

highlight.js

// Previously, https://github.com/timdown/rangy/wiki should be imported/got
var applier = rangy.createClassApplier("highlight");
var highlighter = rangy.createHighlighter();
highlighter.addClassApplier(applier);

document.getElementById('execute').addEventListener('click', function() {
    highlighter.removeAllHighlights();
    highlighter.highlightSelection("highlight");
});