Hmm, this is a good question, I've never thought about it, but after some research I've found a solution for the most part.. I couldn't figure out a way to match spaces so it either highlights a line with #if or with WinActive.
From the menu bar > Language > User Defined Language > Define your language...
This will open a new window, from here select AutoHotKey as your User Language, click Operators & Delimiters tab and in any available Delimiter style put this information in:
Escape: leave this blank
Click the styler button as well to change the background/foreground color
Here's an image with visuals - https://imgur.com/a/XVWAW6Z