Scss not reflected in haml as intended

The style of modules/_index.scss imported later overrides the style set in modules/_tweets.scss, so you can change the import order as follows:

@import "reset";
@import "font-awesome-sprockets";
@import "font-awesome";
@import "modules/index";
@import "modules/tweets";

Consider the following SCSS:

//style.scss
@import "tweets";
@import "index";

// _tweets.scss
.hoge{
  color:red;
}

// _index.scss
.hoge{
    color:blue;
}

Convert style.scss to CSS and you'll see the following (we experimented with https://sass.js.org/):

.hoge{
  color:red;
}

.hoge{
  color:blue;
}

The CSS applies the properties written after the CSS in principle, so color:blue; is applied and color:red; is ignored.