For  1) , the reason why it's off-centered for bookmarks & history is because we align it with the content card, and since bookmarks & history has their side-navs always visible on wide screens, the "center" of the content card would naturally be leaned to the right.

possible solutions:
1) for bookmarks/history, give up aligning it to the center of the card, and just center it relative to the entire page. (This might be considered weird because now the search field is "off-centered" relative to the content that it's searching through).

2) we considered this in the past: for settings/extensions, mimic the bookmark/history's behavior to always have the side-nav visible, and have their search-field lean towards the right like bookmark/history. problem with this: downloads would be the odd one now because downloads doesn't have a side-nav.

3) accept that they're different because their page layout is different