On https://just.systems/, in Japanese Windows, only the character "户" in "用户指南" is displayed in MingLiU (serif), while the other three characters are displayed in a Japanese sans-serif font, making it look ugly.
You should specify lang=zh for that section and explicitly define the default Chinese sans-serif font for each OS for that part only.
After https://github.com/casey/just/compare/master...tats-u:fix-www-top-font?expand=1 is applied:

On https://just.systems/, in Japanese Windows, only the character "户" in "用户指南" is displayed in MingLiU (serif), while the other three characters are displayed in a Japanese sans-serif font, making it look ugly.
You should specify lang=zh for that section and explicitly define the default Chinese sans-serif font for each OS for that part only.
After https://github.com/casey/just/compare/master...tats-u:fix-www-top-font?expand=1 is applied: