Replace text in broccoli-imported css file / ember-cli app

I am currently importing a css file from my bower_components folder in an ember-cli application, e.g.:

app.import('bower_components/toastr/toastr.min.css');

I'd like to modify the CSS in that file before it gets concatenated into vendor.css. How can I do a find a replace so that it ends up in vendor.css?

At this point, I've explored broccoli-replace a bit, but seems that that would only work if I wanted to have toastr.min built as a separate file in my dist folder. I'm not 100% understanding broccoli at the moment, so this could be way off.