I think it would be helpful if the usage of "lo" as a definite article was clarified in the tips and notes. I found from outside sources that, when used with an adjective, it makes the adjective substantive, as an (generally) abstract noun. But I did not find this explained on the duolingo site- I might have missed it, though.
'lo' is supposed to imply the direct object of 'el'- How does it translate to 'you do the opposite'
Here I think "lo" is used as the neuter article, "the." "Lo + adjective" is used to convey an idea. "Haces" = you do, and "lo contrario" = the opposite. Yeah, I know, it is confusing. "Lo" as a direct object pronoun would have to come before the "haces."