fix bad css links
fix bad css links

flaviut/nim-by-example,flaviut/nim-by-example,tmm1/nim-by-example,tmm1/nim-by-example,flaviut/nim-by-example,tmm1/nim-by-example,flaviut/nim-by-example,zhjh1209/nim-by-example.github.io,tmm1/nim-by-example,zhjh1209/nim-by-example.github.io