function _addDynamicFontSize(fontSize) {
        var template = FontRuleTemplate.split("{font-size-param}").join(fontSize);
        less.render(template, null, function onParse(err, tree) {
            if (err) {
                console.error(err);
            } else {
                _addDynamicProperty(DYNAMIC_FONT_STYLE_ID, {
                    ruleText: tree.css
                });
            }
        });
    }
@private
Add the styles used to update the font size
@param {string} fontSize  A string with the font size and the size unit