Press "Undo" to restore the settings that were in use before you opened this notebook page.
Press "Default" to restore the settings to a (hopefully) safe default state.
Note that you can only drop background colors, that is, dropping colors with the
"Shift" key pressed doesn't work, since we have separate fields for the foreground
colors here. The color fields are arranged in a table, so you need to look both
horizontally and vertically to find out what meaning a field has.