Starting in ONTAP 9.12.1, you can specify your preference for the appearance of System Manager. When you first login the default setting is a light theme.
If you click on the icon, in the upper right corner, you can change this to one of three settings.
The left most setting is for the light theme. A light background with dark text.
The middle position is OS position. Default to the theme preference that was set for the operating system’s applications (usually the theme setting for the browser that is used to access System Manager).
And the right most position is the Dark Theme. This is a dark background with a light text.