Kit is not completely themable with sass variables

[Lumrenion]

Prerequisites

Please answer the following questions for yourself before submitting an issue.

• [X] I am running the latest version (2.0.6)
• [X] I checked the documentation and found no answer
• [X] I checked to make sure that this issue has not already been filed
• [x] I'm reporting the issue to the correct repository (for multi-repository projects)

Description

Bootstrap is intended to be rebranded by overwriting only a few theming variables. This behaviour is very convenient and can be easily adapted in the material kit. I noticed several cases where this is not possible.

Expected Behavior

1. Sass variables can be overwritten.
2. Theme colors use specified brand variables. E.g. In _bootstrap-material-design.scss $bg-dark is expected to use bootstrap variable $dark instead of gray-900
3. cards use primary/info/warning/... with lighten functions to create gradient variables. E.g. for .card-header-primary: background: linear-gradient(60deg, lighten($bg-primary, 10%), darken($bg-primary, 10%));

Current Behavior

1. Some Sass variables in _bootstrap-material-design.scss are not defined as !default. E.g. all $bg-* variables
2. In _bootstrap-material-design.scss: $bg-dark: $grey-900;
3. cards use fixed colors to create gradient. e.g. in .card-header-primary: background: linear-gradient(60deg, $purple-400, $purple-700);

[Lumrenion]

Can this issue and my proposed fix (expected behaviour) be confirmed or are there any concerns? I am open for more suggestions and offering to create a PR for this issue once a solution is accepted.

[groovemen]

Hello @Lumrenion,

Thank you for using our products and for this great feedback. I will talk with the team and if everything looks good, we will integrate some of your changes from above and we will update the product.

All the best, Stefan