When sidebar is collapsed, ToC has display and scrolling issues

[simonbasle]

See https://github.com/spring-projects/spring-framework/issues/33122

When the sidebar is horizontally collapsed and one clicks on the ToC button in the sidebar, there are several issues:

• ToC entries are displayed below the breadcrumb
• ToC entries are displayed below the footer content
• the table of content is not scrollable, even if its height is larger than the display area's

Here are a couple screenshots from the Spring-Framework documentation:

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