Make the sidebar fill the vertical space.

[jyasskin]

Also remove a margin-top from the footer that was creating a gap with the sidebar in short windows. Then the footer's shadow disappeared because the z-index was being ignored, which required adding a position property. It's possible we'll want the #content-flex-wrapper to include some padding so things don't run right up to the footer, but nothing I've tested looks particularly bad.

Fixes #3852.

Most of the changed lines are unindenting a block after removing one <div> layer: look at the diff without whitespace changes.

	Short Window	Tall Window
Before
After

[KyleJu]

LGTM. Would you mind including a screenshot after the change?

[KyleJu]

Also Playwright Tests need to be regenerated

[jyasskin]

@dlaliberte, this change shifts the packages/playwright/tests/__screenshots__/chromedash-guide-feature-page_pwtest.js/add-an-origin-trial-stage/create-origin-trial-stage-dialog-* screenshots so that the mask covers a different part of the dialog under test. Is the relevant part of the dialog still visible so that it's being tested?

[dlaliberte]

@dlaliberte, this change shifts the packages/playwright/tests/__screenshots__/chromedash-guide-feature-page_pwtest.js/add-an-origin-trial-stage/create-origin-trial-stage-dialog-* screenshots so that the mask covers a different part of the dialog under test. Is the relevant part of the dialog still visible so that it's being tested?

Answered in chat earlier, but here is a bit more detail. The top part of the dialog popup (dropdown) is covered by the mask, and it would be better to arrange that this didn't happen, somehow, if not too difficult. Perhaps by scrolling the window content, resizing the window, or creating the mask in a way that is below the dialog. Or maybe the screenshot could just focus on the popup element. Not a big deal in any event.

[jyasskin]

Expanding the incubation section moved the history section far enough away that its mask doesn't cover the OT dialog. Thanks for the reviews; I'll merge after the tests pass.