Work items: Improve styling of child items

What does this MR do and why?

Follow-up to Unbox work items (!113838 - merged)

Changes the child items alignment of elements to better go along with other widgets. Also fixes a small bug on darkmode where the :hover styles are not picking up correctly.

Screenshots or screen recordings

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How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. Enable OKRs: rails c, Feature.enable(:okrs_mvc)
2. Create a test objective (http://gdk.test:3000/flightjs/Flight/-/issues [dropdown on the top right, select «New objective»])
3. Create some key results on the test objective from step #2 (closed)
4. Link some tasks on an issue

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.