Implement random background with ASP+CSS

Random background--Whenever you enter this page, a picture will be randomly selected from the specified picture folder to be displayed as the background. The method introduced here is implemented using ASP+CSS.

ASP--From ASP101

Here is a quote:
 Const IMGS_DIR = "/images"
 'Set the address of the picture folder and randomly display any picture in the folder
 Dim objFSO, objFolderObject, objFileCollection, objFile
 Dim intFileNumberToUse, intFileLooper
 Dim objImageFileToUse
 Dim strImageSrcText
 Set objFSO = Server.CreateObject("Scripting.FileSystemObject")
 Set objFolderObject = objFSO.GetFolder(Server.MapPath(IMGS_DIR))
 Set objFSO = Nothing
 Set objFileCollection = objFolderObject.Files
 Set objFolderObject = Nothing
 Randomize()
 intFileNumberToUse = Int(objFileCollection.Count * Rnd) + 1
 intFileLooper = 1
 For Each objFile in objFileCollection
 If intFileLooper = intFileNumberToUse Then
 Set objImageFileToUse = objFile
 Exit For
 End If
 intFileLooper = intFileLooper + 1
 Next
 Set objFileCollection = Nothing
 strImageSrcText = IMGS_DIR & objImageFileToUse.Name
 Set objImageFileToUse = Nothing

CSS

Here is the reference snippet:
 #pic{
 width: 400px;
 height: 300px;
 background: url(<%= strImageSrcText %>) no-repeat;
 margin: 2em auto;
 }

The above code must be added to the header area and cannot be placed in an external CSS file.