Why hover not working

Question

Hover not working
https://code.sololearn.com/WL6wkTCDQc7v/?ref=app

Answer 1

Remove the space as other guys said AND...use " ~ " symbol in between like this:
#a:hover ~ #b

Answer 2

Use "#a:hover" instead of "#a : hover", you have 2 extra spaces

Answer 3

now also not working

Answer 4

thx now working