theme 0.1.6 CSS custom properties not compatible with sass 3.5

[grzuy]

What MDC-Web Version are you using?

mdc-theme 0.1.6

What are the steps to reproduce the bug?

Use sass (ruby sass) latest release (3.5) to compile mdc-theme.scss

$ gem install sass -v 3.5
Successfully installed sass-3.5.0
$ sass _3.5_ packages/mdc-theme/mdc-theme.scss

What is the expected behavior?

That it outputs normally theme CSS custom properties, i.e.

$ sass _3.5_ packages/mdc-theme/mdc-theme.scss | grep "\--mdc-theme-primary:"
  --mdc-theme-primary: #3f51b5;

What is the actual behavior?

Leaves theme CSS custom properties unprocessed

$ sass _3.5_ packages/mdc-theme/mdc-theme.scss | grep "\--mdc-theme-primary:"
  --mdc-theme-primary: map-get($mdc-theme-property-values, $style);

Any other information you believe would be useful?

The reason why this issue isn't affecting MDC demos yet is because node-sass (via libsass) is still in the process of catching up with latest changes in sass-spec.

But it seems that libsass will soon release 3.5 with the same behavior for CSS custom properties. See sass/libsass#2076.

Once the issue linked above is addressed, libsass released and node-sass updated, the demos will suffer from the same issue and the theme properties won't be processed.