We have to define this one in helpers.css because tailwind only
generates a single class but certain things rely on this being
double-class. Command ran:
```sh
perl -p -i -e 's#gt-hidden#tw-hidden#g' web_src/js/**/* templates/**/* models/**/* web_src/css/**/*
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Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>