Left Navigation Sidebar Disappears When Returning to Big Viewport

I checked that…

• … the documentation does not mention anything about my problem
• … the problem doesn’t occur with the default MkDocs template
• … the problem is not in any of my customizations (CSS, JS, template)
• … there are no open or closed issues that are related to my problem

Description

When tabs are enabled, ifyou are in any sub-page that belongs to a tab and you go from desktop layout to mobile, you use the side menu and navigate all the way back to the uppermost navigation level, and you go back to desktop layout, the left sidebar navigation disappears completely

Expected behavior

The left sidebar navigation should remain visible after switching back to desktop layout. For example in your documentation site for MkDocs Material Theme it should look like:

Actual behavior

The left sidebar navigation disappears completely. As can be observed in the HTML inspector for Chrome, all elements nested inside

<div 
  class="md-sidebar md-sidebar--primary"
  data-md-component="navigation"...>
    ...
</div>

have a height of zero, which is why they aren’t visible as can be seen below:

The previously mentioned containing div however still retains it’s height as can be seen below:

Steps to reproduce the bug

I reproduced the bug using your documentation site and also using my own dummy site with no theme overriding or any other customizations. I will add images for both sites so you can see.

Preconditions

• Tabs feature is enabled

Steps

1. Go to Extensions page of Squidfunk’s MkDocs Material site Squidfunk’s My site equivalent

2. Shrink window to trigger mobile layout

3. Click on side menu button to make side menu appear Squidfunk’s My site equivalent

4. Click on back arrow to navigate all the way to the topmost navigation level Squidfunk’s My site equivalent

5. Click outside the side menu to close it

6. Expand window so that it returns to desktop layout

7. Sidebar menu not visible anymore Squidfunk’s My site equivalent

Package versions

For my minimal project:

• Python: 3.6.5 :: Anaconda, Inc.
• MkDocs: 1.1
• Material: 5.1.3

Project configuration

For my minimal project:

site_name: My Docs

theme: 
  name: 'material'
  features:
    - tabs

nav:
  - index.md
  - Extensions:
    - Admonitions: extensions/admonitions.md

System information

• OS: Windows 10
• Browsers:
  • Chrome Version 81.0.4044.122 (Official Build) (64-bit)
  • Firefox 74.0.1 (64-bit)

[squidfunk]

Released as part of 5.1.4

[squidfunk]

Okay, so, first I really want to thank you for providing such a detailed explanation, including the screenshots explaining the problem. It helped to understand the problem at hand. Also, thanks for taking the time to deploy the docs.

Then, I have to apologize for being too quick on that matter - I really thought there’s no easy fix, but we seem to have done it right in the beginning and at some point introduced the bug. For this reason, we can try to re-introduce the missing CSS and see, if this will fix the issues. The _tabs.scss has changed slightly as of v5, so the CSS might need to be a little different. My guess is, that the following CSS might fix it:

@media only screen and (min-width: 76.25em) {
  .md-tabs--active ~ .md-main .md-nav[data-md-level="1"] {
    display: block;
  }
}

If you’d like to take a shot at this yourself, you’re more than welcome to submit a PR 😄