Why is this code not working?

Question

It says 'Uncaught TypeError: Cannot read property 'style' of null Line_3'

Here is the code
https://code.sololearn.com/WB8pAjtZbmPZ/#html

Answer 1

change your class to id and it works(in line 8 and line 23 html section)

OR

Only change getElementById to querySelector in the JS section and it works.

Answer 2

thx