Unable to adjust individual margins when editing a mixin

Issues
1

I am not able to adjust individual margins when making a mixin. When styling individual components, I can click the ‘bottom’ value, then select a margin-value and it is applied to ‘bottom’, however for mixins, when doing the same, the margin is applied to all sides, not just bottom:

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2

Here you can see it in action. If I did this on an element, it would only apply to the one side