I’ll add an option to add custom CSS in a future release.
In the meantime, you can edit the file wp-content/plugins/very-simple-password/VSPFW_view.php using inline CSS tag style=””
Then you can remove that code from your functions, if it’s really bugged.
Please keep in mind that the changes you do to the VSPFW_view.php will be lost upon update, but I don’t plan to update the plugin so soon. The next release will have the custom CSS option.