A11y_AzureNotebooks_Jupyter_EnterExitRiseSlideshow_Keyboard: EnterExitRiseSlideshow Page is not accessible from keyboard using tab key.

[AccessibilityTestingTeam-TCS]

EnvironmentDetails:
Application Name:AzureNotebooks_Jyupter
Login Url: notebooks.azure.com
BrowserDetails:
Edge:Chrome:Version 68.0.3440.106
Operating System:Windows10

Steps to reproduce:
1.Login with the appropriate credentials to azure notebook account.
2.Go to Get started à libraries à Select any of the libraries à click on clone to clone the library
3.Click on Run or right click and select Run to run the notebook.
5.Navigate to the EnterExitRiseSlideshow using the "Tab" key.

Actual:
Issue1:
EnterExitRiseSlideshow Page is not accessible from keyboard using tab key.
Issue2:
"?","Close" and the "Reveal Shortcuts Help" pop-up are not accessible using keyboard.

Expected:
Issue1:
EnterExitRiseSlideshow Page should be accessible from keyboard using tab key.
Issue2:
"?","Close" and the "Reveal Shortcuts Help" pop-up should be accessible using keyboard shorcuts .

UserImpact:
User will face difficulty while traversing through the page.

Attachment:
(https://github.com/jupyter/notebook/files/2400226/A11y_AzureNotebooks_Jupyter_EnterExitRiseSlideshow_Keyboard1.pptx)
(https://github.com/jupyter/notebook/files/2400234/A11y_AzureNotebooks_Jupyter_EnterExitRiseSlideshow_Keyboard2.pptx)

[jtpio]

Closing as there are now different issues tracking accessibility improvements for Jupyter Notebook 7, for example #6800

Thanks!