Fix sponsor logo display on Safari

[delucis]

• Closes Brand logos not visible on Safari 26.5 #2489
• Some difference in SVG rendering in Safari (perhaps specific to <use>?) caused logos to have zero width where they worked in Chromium and Firefox
• This PR fixes that and also cleans up some incorrect CSS syntax in the same component, which @trueberryless noticed now triggers warnings after the switch to lightningcss in Astro 7

Browser Test Checklist

I have tested this PR on at least three of the following browsers:

• Chrome / Chromium
• Firefox
• Android Firefox
• Safari
• iOS Safari

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[trueberryless]

Thanks for the quick follow-up, Chris!

I tested the preview also on iOS on an iPad and the logos are now visible, in comparison to the current live site.

LGTM!