1. Every element defined as a query container has a container badge next to it in the Elements panel. The badge toggles a dotted-line overlay of the container and its descendants.
2. To find and select a container element that caused the query to take effect, hover over and click the element name above the @container declaration.
3. When hovered over, the name turns into a link to the element in the Elements panel and the Styles pane displays the queried property and its current value.

[1] "Container Queries" - Chrome DevTools Docs