openshift-docs: Navigation "hamburger" broken on mobile layout

E.g., https://docs.openshift.com/container-platform/4.9/welcome/index.html

The hamburger menu appears to have it’s z-index too low, and is therefore hidden under the header

Then scrolling down, it finally comes out of hiding

Before finally becoming usable

This was on a Chrome browser, on a desktop machine with the window-width fully minimized. Same thing happened on a Chrome browser on an iPhone.

There’s also an issue I noticed using the “Google Search” app on my iPhone, where the hamburger menu isn’t actually clickable, and doesn’t scroll with page, just stays at the top. I can’t replicate outside of the specific “Google Search” app.