Menu button not visible in dark mode on mobile

[junghans]

Acknowledge the following

• I carefully read and followed the Getting Started guide.
• I read through FAQ and searched through the past issues, none of which addressed my issue.
• The issue I am raising is a potential bug in al-folio and not just a usage question.
  [For usage questions, please use gitter chat instead of raising an issue.]

Describe the bug
In dark mode, the page menu button is not visible.

To Reproduce
Steps to reproduce the behavior:

1. Go to http://alshedivat.github.io/al-folio/ on your phone
2. Click on 'Dark Mode'
3. Menu button not visible, but still here

Expected behavior
Menu button is visible.

Screenshots
If applicable, add screenshots to help explain your problem.
Light theme:

Dark theme:

System (please complete the following information):

• OS: Android 10
• Browser: Chrome

Additional context
Add any other context about the problem here.

[Jongwoo-Shim]

Bug fix : #178

• Tested on mobile and web-dev mode.

[junghans]

Fixed by #178.