Inserter search focus style and alignments

[afercia]

Splitting this out from #1187 that is going to move the inserter search at the top. I'd like to propose two small improvements:

• accessibility: the search field should have a focus style
• readability/design: it would be nice to have the search placeholder/text, the block groups title, and the block icons horizontally aligned; currently, they all have a different left margin/padding which makes visually scanning the content a bit awkard

[jwold]

@afercia

accessibility: the search field should have a focus style

Do you mean something like adding a blue outline?

currently, they all have a different left margin/padding which makes visually scanning the content a bit awkward

Not quite following, can you clarify what you mean?

[afercia]

@jwold re: focus style: yes. as it's standard for all form fields in WordPress. Re: left alignment, see screenshots on the PR #1393