The @position-try CSS at-rule is used to define a custom position try fallback option, which can be used to define positioning and alignment for anchor-positioned elements. One or more sets of position try fallback options can be applied to the anchored element via the position-try-fallbacks property or position-try shorthand. When the positioned element is moved to a position where it starts to overflow its containing block or the viewport, the browser will select the first position try fallback option it finds that places the positioned element fully back on-screen....descriptors specify property values that define the behavior of...a position-anchor property value that defines the anchor element...