improve blog feature image preview

[mfenner]

❤️ Thank you for your contribution!

Description

Added CSS suggested by @ntarocco. Cropped feature image on top and reduced resolution.

Checklist

Ticks in all boxes and 🟢 on all GitHub actions status checks are required to merge:

• I'm aware of the code of conduct.
• I've created logical separate commits and followed the commit message format.
• I've added relevant test cases.
• I've added relevant documentation.
• I've marked translation strings.
• I've identified the copyright holder(s) and updated copyright headers for touched files (>15 lines contributions).
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Frontend

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[mfenner]

Addresses bug described in #210

[saragon02]

LGTM Martin, thank you!