I am trying to use a mdc-component (say mdc-textfield) within a lit element. Looks like I have to import both css and js files into the element.
I'm quite unsure of how to import css into the lit-element.
BTW I use polymer serve
without any preprocessors or compiler.
I recommend to wait for Material Component Web Components
But answering your question, to use MCD you need to use sass, then you will need a pre-compiler. Once you have compiled to CSS you can import it into your component:
I recommend to use a watcher to automatically build the sass files while you are running
polymer serve