There’s a few parts here… I do that red “inset a little bit” on almost 100% of my games. It’s super easy.
Instead of this:
Do this:
And for that inset:
use the preset fullscreen size, but hold down SHIFT and ALT to also set pivot and position and anchors all at once.
now key in the “insets”… like this:
Then just position and anchor entirely within your little “inset.”
You can put insets in your insets, or mix insets with AspectRatioFitters with “Fit Inside”
Here’s more random reading:
Here are some notes on UI Anchoring, Scaling, CanvasScaler, etc:
Usually you need to choose a suitable ScaleMode and MatchMode in the Canvas Scaler and stick with it 100%. Generally if you change those settings you will often need to redo your UI entirely.
I also use this CanvasScalerOrientationDriver utility to make sharing UI for Landscape / Portrait easier. Read what it does carefully.