Focus trap

Focus trap is a web technique to improve accessibility by forcing keyboard focus inside a DOM element, to prevent the user navigating outside that element. This technique normally applies for an open modal dialog, when user interaction is trapped inside the dialog. This makes sense because allowing the focus to escape outside the modal would possibly create a state where the user doesn't know which element is in focus.

Reference

• https://css-tricks.com/a-css-approach-to-trap-focus-inside-of-an-element/