How do I set the URL of a style sheet?

I am using the IE webbrowser control to load a web page we install with our app. I want to dynamically change some of the styles the page uses. Our htm disk-based file has a link of type "text/css" with a href that is a relative path to a css file that is also installed with our app. That style sheet in turn has a "@import url(../../css/theme.css)" entry in it.

Sounded simple enough.

Once I have the document loaded by calling the Navigate method on the web browser control I get the IHTMLDocument2 interface and call get_styleSheets. I get back a style sheet collection and walk the collection. I call to get each item in the collection and get the IHTMLStyleSheet interface on the returned item. I then call IHTMLStyleSheet::get_href to get the href and examine it to see if it has "theme.css" in it.

Since one style imported others, I also call IHTMLStyleSheet::get_imports to get any imported sheets and call the same routine (recursively) to walk the sheets and examine the URLs.

When I find the URL I want to replace, I call IHTMLStyleSheet::put_href with the relative path to the style sheet I want (it is in the same directory as theme.css so I just replace the name leaving the path intact).

When I am done and the page displays, the style sheet used is still the original style sheet. So after I called put_href, which is returning a HRESULT of S_OK, I have another line of code for debugging where I call get_href again. I expected to see the new href I just set. Instead, the same href comes back.

I tried calling the web browser control's Refresh() method but that made no difference. I also obtained the IHTMLDocument3 interface and called recalc( VARIANT_TRUE ). Still the href is returned as the original href. I have walked all the style sheets and there is only one "theme.css" so I am replacing the only one with the sheet I want. I have examined the string I am passing in to put_href and it is the url that I want.

So why doesn't put_href work as advertised? Why would get_href not return what I set via put_href?

HRESULT WalkStyles( IHTMLStyleSheetsCollectionPtr pStyles )
{
	if( pStyles )
	{
		IHTMLStyleSheetPtr pSheet;

		long lNumStyleSheets = 0;

		pStyles->get_length( &lNumStyleSheets );
		for( long index = 0; index < lNumStyleSheets; ++index )
		{
			IDispatchPtr pDispStyle;

			_variant_t vIndex(index);
			_variant_t vDisp;

			pStyles->item( &vIndex, &vDisp );
			if(  pDispStyle = vDisp )
			{
				pSheet = pDispStyle;

				BSTR bstrhref = 0;
				BSTR bstrnewhref = 0;

				pSheet->get_href( &bstrhref );

				CString strThisCSS = bstrhref;
				if( !strThisCSS.IsEmpty() )
				{
					strThisCSS.MakeLower();

					int FindIndex = strThisCSS.Find(L"theme.css");
					if( -1 != FindIndex )
					{
						strThisCSS.Replace(L"theme.css", L"themeblack.css");
						_bstr_t bstrNewStyleURL = strThisCSS;

						pSheet->put_href( bstrNewStyleURL );

						// No change! Debug code - call again to get the href.

						pSheet->get_href( &bstrnewhref );
					}
				}
				IHTMLStyleSheetsCollectionPtr pImportStyles;

				pSheet->get_imports( &pImportStyles );
				if( pImportStyles )
				{
					WalkStyles( pImportStyles );
				}

				if( bstrhref ) SysFreeString( bstrhref ); bstrhref = 0;
				if( bstrnewhref ) SysFreeString( bstrnewhref ); bstrnewhref = 0;
			}
		}
	}

	return S_OK;
}

R.D. Holland