[J5.2] Cassiopeia - Only add margin to system message container if it contains a joomla-alert

[coolcat-creations]

Pull Request for Issue #40639.

Summary of Changes

Added a :has rule to control the margin of the system-message-container if it does not contain a tag
:has selector is supported by all modern browsers

Testing Instructions

login with wrong credentials in your cassiopeia frontend.
A system message appears that the login data is wrong
Click the close button to hide the message

Actual result BEFORE applying this Pull Request

After hiding a system alert, a margin of 1rem remains

Expected result AFTER applying this Pull Request

After hiding a system alert, the margin is not present anymore

Link to documentations

Please select:

• Documentation link for docs.joomla.org:

• [x ] No documentation changes for docs.joomla.org needed

• Pull Request link for manual.joomla.org:

• [x ] No documentation changes for manual.joomla.org needed

[ghost]

I have tested this item ✅ successfully on 97d0209

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44222.}

[ChristineWk]

I have tested this item ✅ successfully on 97d0209

with NPM Package

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44222.}

[richard67]

RTC

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44222.}

[brianteeman]

I have tested this item ✅ successfully on 97d0209

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_{This comment was created with the J!Tracker Application at issues.joomla.org/tracker/joomla-cms/44222.}

[pe7er]

Thanks @coolcat-creations !

[coolcat-creations]

Thank you for merging!