Add opacity and update Item-list

[Daksh14]

This PR adds opacity classes and upgrades the item lists. Also updated documentation for both of them

[ArtOfCode-]

Deferring to @luap42 here.

[luap42]

Looking at the docs preview:

• It's too large (was already said, just repeating here for completeness).
• I think the effect on the "accepted answer" block is too heavy. I'd go with a lighter effect.
• Don't use buttons just to show icons. Use utilities for creating visual effects, but buttons are for interactions.

[Daksh14]

@mattjbrent and @cellio are currently working on the layout part and finalizing it. I'll have to wait and then replicate it.
Also for an accessibility reason, one could hover over them and know about the number of views, answers, etc. If that's possible with the utilities then I'll see

[cellio]

We don't want to grab ~35% of the horizontal space for stats widgets; that has a bad effect on the title.

We don't have the "accepted answer" concept, so we don't need to style that. (If we want this kind of highlighting for something else, we might want a less-assertive color.)

I like moving the votes over to the right, so the first thing you see is the title not the score. There's a proposal to do that on question pages too. @mattjbrent has some ideas about this for the question list; it's possible we won't even show a score number in the list. Maybe we want to abstract it away into vaguer "very positive - positive - meh - negative" scale. Alternatively (and my original proposal), we'd show +N/-M.

The gray last-modified text is very light; probably does not meet accessibility guidelines.

Support for tooltips on most page elements would be good for accessibility. (Also, any essential images should be backed by alt text for screen readers. But decorative graphics shouldn't as it just gets in the way for the user.)