The Parcel editor has both a dark and a light theme. The dark theme is enabled by default. You can change the theme by selecting Preferences in the left side bar and navigating to Theme in the popup preferences window. Your choice of theme is synced with your account - wherever you log-in, you'll experience the same theme.

Silent video of the full Parcel window. The cursor navigates to and clicks on the Preferences button in the left sidebar. The preferences dialog opens, and the user navigates to the "Theme" section. There is a dropdown menu with two options: "Parcel Dark" and "Parcel Light". The user switches from "Parcel Dark" to "Parcel Light". The dark background color of the webpage becomes white.
Screen recording showing the switch from dark mode to light mode

This should not be confused with light/dark mode in the preview.