PageLayout’s LeftSidebar has a Flyout feature (https://atlassian.design/components/page-layout/examples#left-sidebar).
When hovered over a closed sidebar, it expands over the Main content, providing quick access to options in a sidebar.
The issue is that while LeftSiebar has z-index set to 1, Main does not have any z-index set. Main (https://atlassian.design/components/page-layout/code) should have z-index set to 0. This way LeftSidebar would be displayed above Main when the Floyout feature is activated, does not matter what elements Main contains,
Currently if some element inside of Main has a z-index set to >=1, this element is visible over the LeftSiebar in a Flyout mode.
Below is an example from Atlaskit documentation, where I’ve added an element inside Main with z-index set to 1.