can't change submenu "group-content" font size

Ηι!
Thank you for your excellent product! I m newbie css3 mega menu user.
I have this problem:

although this works fine in style.css
#jux_megamenucss3 .megamenu ul.level0 li.megacss3 .group-content{
font-style:italic;
}

this one NOT:

#jux_megamenucss3 .megamenu ul.level0 li.megacss3 .group-content{
font-size:13px;
}

So, i can't change the submenu (group content) FONT SIZE (and other font properties) in any way...
I'd spended much time on this, but it not solved!

Thank you in advance,
John Gr

Thank you for your replay and excellent response time!!

Basically i want to change group-content Font Size, NOT tilt!

(i have not any problem about tilt, and easy and succesfully i changed with this code:
#jux_megamenucss3 .megamenu ul.level0 li.megacss3 .group-content{
font-style: italic;
} (without "li.megacss3")

BUT CANNOT change the Font Size of group-content with code below:

#jux_megamenucss3 .megamenu ul.level0 li.megacss3 .group-content{
font-size: 8px;
} (Note: this, not work with ".group-content li.megacss3" too!)
As you know, changing Font Size is important for flexibility, when building a web site, so, any help will be valuable!
Thank u in advance!

John GR