Set Sass sourceMapEmbed

I want to have embedded sourcemapping for my css files (for development only). I'm using Laravel Mix 6. Following the documentation on sas options, I've added the following to my webpack.mix.js file:

mix.sass('resources/assets/sass/app.scss', 'public/css', { sassOptions: { sourceMapEmbed: true } })

But when I run npm run dev, I don't get any errors, but all I see in Chrome DevTools under Style is app.css. Am I doing this correctly?