chore: build sass to a seperate file for each chart
chore: build sass to a seperate file for each chart

This is so that the sass file has its own name. Previously, we were
running into issues where `_styles.scss` wouldn't work because there was
a `styles.css`.

DensityCo/charts,DensityCo/charts,DensityCo/charts,DensityCo/charts