CSS Deactivate an Overview of a Parenting Class


I have two style sheets in page.html:
parent.css and child.css

In parent.css I have:

#MAINTable tr:hover

I need to deactivate this from child.css

I'm doing:

#MAINTable tr:hover{text-decoration: none !important;}

But this is not working. What am I doing wrong?

Thanks a lot!

PD: Sorry if the question was too simple, learning CSS here

You can try this to overwrite the background:

#MAINTable tr:hover {
    background: transparent;