Plugin changes the appearance of KeePass, to make it look better at night.
You can enable it using hotkey
CTRL+T or using the menu
Tools -> DarkTheme.
The plugin allows you to create your own theme.
KeePass was created using standard Windows controls, which unfortunately were not designed for easy customization. They are extremely resistant to any attempts to change their appearance, especially from a plugin which has no control over their creation.
Therefore the plugin is not perfect and will never be, but is good enough to use it.