Styles are applied when page load is finished, however loading time of page may be long.
If Stylus can run at document start, I don't need to wait page load finished.
Can Stylus run at document start?

updated:
Oh, I find the problem. It is my fault.

I used 'max-width: calc(100vw - var(--scrollbar_vertical_width));' in Stylus.
And the value of '--scrollbar_vertical_width' is set using javascript (Tampermonkey).
i.e. window.addEventListener("load", function() {/* calculate scroll bar size */})

The value is set on loaded, so before loaded the value is invalid and the style will go wrong.
Now I change 'load' to 'DOMContentLoaded', it is fine.