Vim syntastic scss error, doesn't read the imported files

Question

How to make vim syntastic to read the imported files? Currently my scss directory files like this:

scss/
----custom.scss
----style.scss
----variable.scss

I import all the scss file into style.scss, so the style.scss contains:

@import 'variable';
@import 'custom';

That's fine, then in my variable.scss, e.g I make a variable of color $primary-color: #3298df;. Then in my custom.scss contains:

a, p {
    color: $primary-color;
    font-weight: bold;
}

The vim syntastic will notify me an error saying that Undefined variable: $primary-color, but if I build the scss file and run in the browser, it works fine.

Any clue for the vim syntastic configuration ?