Themes: Remove unnecessary spacing on auto-loading homepage confirmation modal.

[blackjackkent]

Changes proposed in this Pull Request

• The auto-loading homepage confirmation modal on the theme showcase has a min-height on its description paragraph in mobile to prevent controls jumping around when changing the selected radio button (which changes the text).
• This is not necessary on desktop and in fact adds extra spacing that looks weird, so this update removes it from medium-breakpoint screens and above.
• This PR also fixes an issue which was preventing demo homepage preview images from completely filling their container.

Before:

After:

Testing instructions

• Navigate to Theme Showcase -> Click on three dots menu of a recommended theme (Ideally TwentyTwentyOne since it has a colored background) -> Click activate
• Verify that the modal popup does not have unnecessary space between description paragraph and buttons.
• Verify that right-hand preview image fills whole container.

Related to p1624477808051100-slack-C0202PMUXLJ

[sixhours]

The right-hand screenshot does fill the container now, but it's stretched. I'm fiddling with the CSS to see if I can find the happy medium between the iframe and the screenshot.

[matticbot]

Link to Calypso live: https://calypso.live?image=registry.a8c.com/calypso/app:build-8762
Link to Jetpack Cloud live: https://calypso.live?image=registry.a8c.com/calypso/app:build-8762&env=jetpack

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~9 bytes added 📈 [gzipped])

name    parsed_size           gzip_size
themes        +73 B  (+0.0%)       +9 B  (+0.0%)
theme         +73 B  (+0.0%)       +9 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/6068542

Thank you @blackjackkent for including a screenshot in the description! This is really helpful for our translators.

[a8ci18n]

Translation for this Pull Request has now been finished.