[REF] Add in css classes to make the save and preview button on the C…

[seamuslee001]

…ontribution Page widget settings form look consistant with the other buttons on the page

Overview

This adds in CSS classes to fix the look of the Save and Preview button on the Contribution Page Widget settings

Before

After

ping @eileenmcnaughton @agh1

[civibot]

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[eileenmcnaughton]

@agh1 is this good to merge?

[agh1]

Yeah this form needs a lot more in-depth attention but this change does nothing to interfere with that and improves the consistency. Looks good by me.