Change selected text color bg

HTML

<div>
<p>The quick brown fox jumps over the lazy dog</p>
</div>
<br />
<input id="changeColor" type="button" value="Select text and Change Style" />

JavaScript

function selectHTML() {
    try {
        if (window.ActiveXObject) {
            var c = document.selection.createRange();
            return c.htmlText;
        }
    
        var nNd = document.createElement("span");
        var w = getSelection().getRangeAt(0);
        w.surroundContents(nNd);
        return nNd.innerHTML;
    } catch (e) {
        if (window.ActiveXObject) {
            return document.selection.createRange();
        } else {
            return getSelection();
        }
    }
}

$(function() {
    $('#changeColor').click( function() {
        var mytext = selectHTML();
        $('span').css({"margin-bottom":"10px"});
    });
});