I have the following in my Sway configuration and can't get it to work on anything other than Chromium and Electron apps, for some reason:

   # window borders
   for_window [class="^.*"] border pixel 1
   default_border pixel 1 

Apparently new_window is deprecated. Not quite sure why it acts like this, but it's nice to reclaim those extra pixels, especially since Waybar displays the window title anyway.