The :focus-within pseudo-class applies to elements for which the :focus pseudo class applies. An element also matches :focus-within if one of its descendants in the flat tree (including non-element nodes, such as text nodes) matches the conditions for matching :focus.
Docs: https://developer.mozilla.org/en-US/docs/Web/CSS/:focus-within
Samples: http://codepen.io/anon/pen/xOLJym https://blogs.igalia.com/mrego/files/2017/05/focus-within-demo.html https://blogs.igalia.com/mrego/files/2017/05/focus-within-menu.html