fix(typography): set `CodeBlock` background to `background.recessed`

Description

Sets the background color for CodeBlock to background.recessed in order to offset from the default background in dark mode.

[x] :ok_hand: design updates will be Garden Designer approved (add the designer as a reviewer)
[x] :globe_with_meridians: demo is up-to-date (npm start)
[ ] :arrow_left: ~renders as expected with reversed (RTL) direction~
[x] :black_circle: renders as expected in dark mode
[x] :metal: renders as expected with Bedrock CSS (?bedrock)
[ ] :guardsman: ~includes new unit tests. Maintain existing coverage (always >= 96%)~
[x] :wheelchair: tested for WCAG 2.1 AA accessibility compliance
[ ] :memo: ~tested in Chrome, Firefox, Safari, and Edge~