Reader: file block is missing spacing and the download button isn't styled

[designsimply]

Steps to reproduce:

1. On the web, create a new post.
2. Add a paragraph.
3. Add a file block.
4. Add another paragraph.
5. Publish the post.
6. View the post in the Reader.

Result:

• No space between the filename and the download button.
• Download button is missing styling.

WPAndroid Reader	WPAndroid Reader	Chrome Android 10

^{Tested with WPAndroid 14.7-rc-2 on Pixel 3 Android 10.}

[designsimply]

Related button block issue: #11679.

[ashiagr]

Should be addressed in Automattic/wp-calypso#43595