Bug - missing background on web alerts

[muling]

Describe the bug

Contextual web alerts no longer have a background colour. This makes it less accessible unless the background is white and it is less noticeable to users.

Note: If your request is related to security, please do not open a publicly visible "issue"; refer to SECURITY.md.

To Reproduce

N/A - it's more of a critique of the new style

Example

Current behaviour

No background colour makes it difficult to read and less noticeable.

Expected behaviour

We would like to keep the background colour from previous WET template versions. Or make it optional to turn on. Otherwise, we have to add our own custom styles.

Screenshots and/or logs

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Desktop (please complete the following information):

ALL browsers, versions.

Smartphone (please complete the following information):

ALL.

Additional context

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