Huge Buttons with Simple Donate
With a default-ish theme, the SimpleDonate extension intends to make the form elements bigger and more clicky. In this case that has not worked out - possibly because of other styles introduced by your theme or other plugins.

However: those button styles you're seeing are coming from the SimpleDonate extension. And that's OK - you can address this by overriding with your own theme's CSS. Even just adding a style which cleared the buttons into rows of three would improve what you're seeing.

The liberal use of !important in SimpleDonate's CSS may be a sticking point when overriding the extension's builtin styles. If I had to make that CSS work, the first thing I'd do would be replace every instance of !important with an appropriate CSS selector (and submit the PR back to SimpleDonate).