The selector ".sans" was not found

[chaoyuan899]

error sass/screen.scss (Line 93 of sass/base/_syntax.scss: "html .gist .gist-file .gist-meta" failed to @extend ".sans".
The selector ".sans" was not found.
Use "@extend .sans !optional" if the extend should be able to fail.
)
Compilation failed in 1 files.

[humburg]

It is possible to resolve this by implementing the change suggested by the error message, i.e. add "!optional" for the relevant @extend directives in sass/base/_syntax.scss (there are two more). Everything seems to work fine after that but I have no idea whether the effect is as intended.

[chaoyuan899]

Thanks.