sass !default for configurable variables

[alifr]

Expected behaviour

The variables in the highcharts/css/highcharts.scss should have the !default flag. Then we could import the scss file into our project and override the theme styles without having to duplicate the entire file.

Example

@import 'https://code.highcharts.com/5/css/highcharts.css';

$colors: #40bfa2 #984e9b #fb7830 #01acc8 #CDAED1 #82368C #AAAEB2 #565E65 #EF92A5 #DF264C #565E65 #A8E9F3 #FFBA9D #FF763B #95FEDB #27CAE1;

[TorsteinHonsi]

Thanks for your suggestion!

We had a pull request for this a couple of months back, but it broke our build system because the SASS variables are also inserted directly into the generated source code. So we'll have to fix that first. See #6009.