Better size balance between portrait and landscape images

[Toutouwai]

Also fixes invalid !important rules that were missing an exclamation mark.

[Toutouwai]

Before:

After:

I'm not a big fan of the busy checkerboard background (would prefer a solid light grey myself) but thought I'd better leave that alone.

[anilex]

Without an intention to be in opposite side, I prefer the "before" layout, no matter if "After" is with or without solid gray background.

[horst-n]

I'm against the checkerboard, as it doesn't work with transparent images, what also doesn't work with solid colors. But definetly there is a need for better communication of the dimensions / proportions of the images in the thumbnail views! There are some examples in the forum already, with screens and explanations: https://processwire.com/talk/topic/13808-background-for-png-images/#comment-124313 (also following and/or above posts)