import css use scss

[yozman]

how can I import my css file use scss import?

I want to use like this

// app.scss
@import "theme.css";

button {
  @extend .btn;
}

// theme.css
.btn {
   // ...
}

but there is an error:
Parse error: "button" failed to @extend ".btn". The selector ".btn" was not found.: line: 4
I found scssphp parsed @import use css not scss,
could you tell me what should I do?

[robocoder]

Not supported. See #402

[yozman]

@robocoder
I read the article
but really need that feature

for support just need change 1 line
\Leafo\ScssPhp\Compiler::findImport#3221

to

if (! preg_match('/^https?:\/\//', $url)) {

[yozman]

@robocoder
I have an new idea
how about use a config to toggle support import css?