Border thickness not changing in i3wm

I lost all my window manager-related configs so I’m starting from scratch. I have looked at the documentation. I tried this and I didn’t get errors:

new_window pixel 12 
for_window [class=".*"] border pixel 12

But the thickness doesn’t change. I believe I used these same commands in my last config for a different OS, and it worked. I’m wondering if there’s a weird interaction with Qubes.

Edit: confirmed on another OS that these commands work.