When clicking to "Digital Input", there is no arrow button to back to previous tutorial

[Helen09]

Repro steps:

1. Navigate to https://makecode.adafruit.com/beta
2. Scroll down the scroll bar to the bottom of the page
3. Click on tutorials one by one

Expected result: When clicking to "Digital Input", there should have arrow button to back to previous tutorial

Actual result: When clicking to "Digital Input", there is no arrow button to back to previous tutorial