Lukas,

Not sure if this has already been reported,
	(WAUrl new)
		addToPath: 'files';
		addToPath: 'basic.css';
		asString
gives
	'/files/basic.css/'

If the css stylesheet is refering to images in the same file library,  
then you need something ugly like this
	url(../bg.jpg)

Instead I am hacking this (ugly too but not as much) in  
WAUrl>>pathString for the trailing slash.
	(path last includes: $.) ifFalse: [stream nextPut: $/]

Cheers,
Michel.