fix: Add poster size styles

[mister-ben]

Description

Adds styling for the img el in the poster's picture so it scales correctly.

Requirements Checklist

• Feature implemented / Bug fixed
• If necessary, more likely in a feature request than a bug fix
  • Change has been verified in an actual browser (Chrome, Firefox, IE)
  • Unit Tests updated or fixed
  • Docs/guides updated
  • Example created (starter template on JSBin)
• Reviewed by Two Core Contributors

[codecov]

Codecov Report

Merging #8022 (169fdc8) into main (84062c3) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main    #8022   +/-   ##
=======================================
  Coverage   82.67%   82.67%           
=======================================
  Files         110      110           
  Lines        7342     7342           
  Branches     1772     1772           
=======================================
  Hits         6070     6070           
  Misses       1272     1272           

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