Confusing custom theme asset paths

When editing `theme/style.css` or if you want to import another css file, you are supposed to put the other file in `theme/assets/custom` folder.

So you have an import like:

```
@import url("./colors.css");
```

But you need the `colors.css` to actually be in `theme/custom/colors.css`.

Same story with script.js.

This is not sensible.