To create a back component, use the Back() function on any control
Hover and Focus states are handled by Power Apps itself as long as you fill in all of the necessary properties (HoverBorderColor, HoverFill, HoverColor, FocusedBorderThickness, FocusedBorderColor, etc) for each control.
You can see the guidance for creating accessible apps for some info on what you should be aiming for, there are also a few other sub-sections you can find on the left-nav-tree within the accessible section that can provide more info - I particularly suggest looking at all of them but definitely this list of limitations when building accessible canvas apps
I have also built an App template that allows you to define colours and properties for controls programmatically that then apply to all future created controls (modern controls are excluded as the Power Apps team has done these via PCFs which don't have the same ability to be modified) - video of my talk around this can be found here:
Sancho Harker - Instant Accessibility using a Theming Template - YouTube
Mike Hartley has also done a simplified version that allows you to choose WCAG-compliant colours/fills here:
Power Apps, Accessibility, and WCAG - Hart of the Midlands
Hopefully this will all be useful to you, I know its a lot but the topic isn't perfectly-covered by the msdocs 🤷
Cheers,
Sancho
