Custom Class Text Widgets is a multi text widget that allows you to also define a custom class for the widget meaning you have better control over the styling of the elements.

WP Christmas Class allows you to dynamically add a custom CSS class to your body tag during a date range of your choosing.

Simple plugin to add custom CSS class to Elementor image.

Lets you add a custom CSS class to each widget instance.

Extends the Gravity Forms plugin - Adding a new field type to wrap field items in a div with custom classes.