Add some CSS helper classes for colours

• danger
• warning
• success
• ...

changed milestone to %2.0a1

added part::frontend label

mentioned in merge request AlekSIS-App-Chronos!31 (merged)

Maybe we can use something like this:

https://materializecss.com/color.html

• danger: red lighten-2
• success: green lighten-2
• warning: yellow lighten-2

The lighten variants are good for background colours, for foreground it's too light. There I will use the standard variant.

Yup, but maybe its to dark for table columns.

I will see.

Funnily enough, Materialize's SCSS defines colour variables for success and error, but they are never exposed.

changed milestone to %2.0a2

created branch 163-add-some-css-helper-classes-for-colours to address this issue

mentioned in merge request !139 (merged)

closed via merge request !139 (merged)

mentioned in commit e26f8831

added part::frontend label