String Writer

In most cases, you will not be publishing the binary files (images/css/js) in the same location of where you publish pages. As a good practice, these external files will be stored in separate folders. In such cases, you will need to  specify path (relative) in the page DWT template.

Generally external css files will be declared like

<link href="/styles/main.css" rel="stylesheet" type="text/css"/>

This would work only if you have styles folder immediately after server path.

http://<server>/styles/main.css

In Tridion, default publication URL is “/” but if you have specified any path in the Publication,  you will need to append that path also. It should be accessed like.

http://<server>/<pub url>/styles/main.css

The below C# TBB will get the publication URL of the current publication.

//gets the current session object
 Session session = engine.GetSession();
 //gets page object from the package
 Item item = package.GetByType(ContentType.Page);
 //gets TcmUri object of Page
 TcmUri tcmObj = new TcmUri(item.GetValue("ID"));
 //generate tcm string format with publication id
 string publicationId = string.Format("tcm:0-{0}-1", tcmObj.PublicationId);
 //gets publication object from the current session
 Publication publication = new Publication(new TcmUri(publicationId), session);
 //writes the publication URL into the package
 package.PushItem("PublicationUrl", package.CreateStringItem(ContentType.Text, publication.PublicationUrl));

As you aware, variable “PublicationUrl” will be included in the package so this variable is accessible when you include this TBB on your page template.
Now you need to call this variable on the page DWT like below,

<link href="@@PublicationUrl@@/styles/main.css" rel="stylesheet" type="text/css"/>