Fix post image alignment and caption size

[backspace]

These are some changes requested by a blog post author 🤓

Here’s an example of the post image alignment change:

And the caption being smaller:

These screenshots are from Percy (as in progress in #41) but I’m manually pasting them here until I can get the WPCH organisation set up in Percy.

[farfamahar]

Nice. My fix before was "upload bigger pictures" 😅. This is much better.

[backspace]

hah classique 😆