css { content: "text"}, how do I add tags?

Question

The content declaration cannot add tags to the page (tags are structural); additionally, CSS is meant for presentation changes, not structural content changes.

Consider using jQuery, instead, such as:

$(".HeaderName").after("your html here");

If you need that extra tag only to make the added text red, just do this:

.HeaderName:after{
    content: "text";
    color:red;
}

Tested on Chrome.

You can't insert tags using content: in CSS. Here is the relevant part of the spec; see the 'content' property in the CSS 2.1 spec.