This image shows a dialog that is clearly in the foreground. It draws the user's attention with the darkening of the page behind it. 

University of Michigan - Ann Arbor

Figure-ground can be used to show the user what they should be paying attention to. This can be done with dialogs, navigation panels, and use of color. 

Figure-Ground in Interaction

"What are Gestalt Principles?" Interaction Design. https://www.interaction-design.org/literature/topics/gestalt-principles

Gestalt Principles of Design

Example 1

This image shows how color can make fields pop into the foreground.

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