This is not just a problem with the libCompiler, but this situation (the double slash //) also exists with the delivered dhtmlx.css in the dhtmlx_pro_full.zip file.
I experienced the same problem and used the same solution (search/replace the extra slash).
Ah! The reason is most likely because the dhtml.css you have (and if I’m right there’s also a dhtml.js file in the same package directory) were both created by the lib compiler.
You’ll probably find the .css for the individual component is correct. The lib compiler bundles everything together into a dhtml.css and dhtml.js and it seems this adds the extra ‘/’