Press F5 to open a new window with your extension loaded.
Open File > Preferences > Color Themes (or Code > Preferences > Color Theme on macOS), and pick Tokyo Hack.
Open a file that has a language associated. The languages' configured grammar will tokenize the text and assign 'scopes' to the tokens. To examine these scopes, invoke the Inspect TM Scopes command from the Commmand Palette (Ctrl+Shift+P or Cmd+Shift+P on Mac) .
You can relaunch the extension from the debug toolbar after making changes to the files listed above.
You can also reload (Ctrl+R or Cmd+R on Mac) the VS Code window with your extension to load your changes.