Added !default to variables to fully utilize scss

[Nazin]

That way I can include tagify scss in my project directly and easily change the variables.

i.e.:

$tag-bg: blue;
@import '../../node_modules/@yaireo/tagify/src/tagify';

[yairEO]

Tip for importing SCSS files from node_modules: parcel-bundler/parcel#1800 (comment)

[yairEO]

Thanks! excellent idea!