Results 2 issues of volnet

当css链接写成``因为部分站点可能会使用https,从而导致被浏览器阻止,而该地址支持https,只需将它去掉即可。

### Preflight Checklist * [x] I agree to follow the [Code of Conduct](https://github.com/jgraph/drawio-desktop/blob/master/CODE_OF_CONDUCT.md) that this project adheres to. * [x] I have searched the issue tracker for a feature request...

wonfix