Created attachment 252443 [details] [review]
patch to address the issue

This should fix the issue. I was unable to find how regular buttons do this specifically, but this seemed to do the trick.

Created attachment 252444 [details]
screenshot with patch in action

This is a tricky one - the button is not actually taller than the other, but the other embeds an 1px semi-transparent shadow in its bottom border.

The ideal fix would be to prepare a similar asset for this button, and use border-image like we do for regular buttons instead of border-color. Otherwise, with your fix, you'll get a weird effect towards the bottom, where the curvatures of the box-shadow and the one of the border don't perfectly collide.

This would also be needed for the destructive button introduced in #706385

Yeah, indeed.

I think I figured this out now. Patch coming soon.

Created attachment 252474 [details] [review]
patch to address the issue v2

Second try.

Review of attachment 252474 [details] [review]:

Looks much better - still some comments below.

::: themes/Adwaita/gtk-3.0/gtk-widgets-borders.css
@@ +262,3 @@
+.suggested-action.button,
+.suggested-action.button:active {
+    border-image: -gtk-scaled(url("borders/button-border-suggested.png"),url("borders/button-border-suggested@2.png")) 3 3 4 3 / 3px 3px 4px 3px stretch;

You need to copy the selectors for these borders - possibly including a different asset - for the dark theme variant in gtk-widgets-borders-dark.css

@@ +269,3 @@
+}
+
+    border-radius: 3px;

Comment should say "destructive" instead of "suggested"

::: themes/Adwaita/gtk-3.0/gtk-widgets.css
@@ +3115,1 @@
     border-width: 1px;

I think you should be able to remove these border sections completely from these selectors in gtk-widgets.css, as you define the border already in gtk-widgets-borders.css

Created attachment 252497 [details] [review]
patch version 3

Addressed review.

Review of attachment 252497 [details] [review]:

Is this on top of the previous patch? Can you squash them together when you commit?

::: themes/Adwaita/gtk-3.0/gtk-widgets.css
@@ -3113,3 @@
-    border-style: solid;
-    border-color: transparent;
-    border-width: 1px;

I think you're still missing to remove these from the destructive button selector.

Created attachment 252514 [details] [review]
patch v4

Man, I'm really the worst with git, but I hope this works.

Yeah, patch looks good! I squashed the commits into a single one for you and pushed it to master.
Thanks!

Did all the images got included as well?
I can't see the borders under OSTree now.

Hmm, we forgot to add them to the theme GResource. I pushed another fix to git master now, can you please test the latest?

That did the trick!
Everything working as expected now.