What’s the 'Layout' custom style?

It's a style that's applied to elements that have a container. Use it to style the container or target and style any child elements.

The layout custom styles appears in the Custom style drop-downs for elements that are a container or have a containing div element. This includes Columns, Containers, Slider containers and the WYSIWYG element.

You can use the Layout custom style to style the container and to style any child elements of the container using Child selectors.