[Theme: TwentyTwelve (Child)] Button shrinks when pressed

Looks like some padding causing the issue.
When you define styles for that submit button, just use an additional selector for the :active class.

What exactly does that mean, and what would it look like?

Try a CSS forum like https://CSSCreator.com/forum for this level of CSS support.

How do I report this as a theme bug?

You’d need to first produce the issue on theme’s demo website https://wp-themes.com/twentytwelve

Well, that would be as simple as just clicking the Search button, and the content underneath is pulled up by 1 pixel or something on the active: state.

That’s not the same issue as yours and it is not a bug. It is intentionally set by removing the border on the active state. You had a padding issue.

The issue still persists when I view my website live with the original Twenty Twelve theme. I don’t know how the clear and submit buttons on the theme preview page are rendered, as they seem to work fine in contrast to the search button (i.e. not pulling up the content underneath).

I used the following code to render my button:

<input type="submit" value="Press Me" />

On that note, I did manage to fix the resizing issue for my child theme yesterday, after dabbling with the code and changing about two or three values that were related. Can’t remember what they were at the moment, though.

Anyhow, my issue now is that the border on the left of the button doubles when it’s pressed. Can’t really figure out what’s causing that either.

I suspect it has something to do with your syntax error on 183 of your Child Theme stylesheet.

Yeah, I just noticed that one of my declarations was missing a semicolon. My button works perfectly now. ??