Also shown above the Stage are three purple context tabs: Format, Style and FX.
Select the three-dot menu icon.
NOTE: We are showing the menu here in order to present a complete picture. To save a step as you work, you can also select the Format, Style, and FX context tabs directly.
The Theme's default color options are shown in the Color section.
Select the down arrow on that section to view the full list of options.
For this example, select the white option in the Lighter row. (You can't see the Aa symbol as there isn't enough contrast between the text color and the panel color.)
Select the Stage background.