`calc` with navigate is invalid in some preprocessor.

[Chen Minglong]

7.css/gui/_window.scss

Line 72 in a1355c0

 margin-top: calc(-var(--window-spacing) - 1px); 

detail in this post.

https://stackoverflow.com/a/25205523/3646724

so you can use margin-top: calc(0 - var(--window-spacing) - 1px); instead

[Khang]

Hey mate, thanks for pointing that out, didn't know of such problem. I will check the PR.