[4.0] system css

[brianteeman]

This PR removes the reference to background images that are not part of the release.

Code review should be fine

Pull Request for Issue #32929

Any other comment about this css is off topic and will be ignored

[richard67]

I have tested this item ✅ successfully on c246b7b

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[dgrammatiko]

I have tested this item ✅ successfully on c246b7b

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/33258.}

[richard67]

RTC

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[Quy]

Thanks.

[brianteeman]

Thank you