scss compilation

I just started my custom theme, named “smart_theme”, and something went wrong.
I did basic thing:
Inherited reindeer like this:

Made style.scss like that:

And left “addons.scss” almost empty, it contains this row:

@mixin addons { }

Pure reindeer style is ok:

But after inheritance in my custom theme, closeable tabs are broken, just a bit.

Is that me, or is that something works not properly?