Check code for me

Hello,

I have the following code in my custom css. But I can’t get the main menu font to change size. Is there something wrong here? Thank you!!
This is what I have in custom css. Is this wrong? I really have to get this fixed.
#header{
opacity: 0.5;
}
@media only screen and (max-width: 480px) {
h1 { font-size: 25px !important; }
#header_meta .container {
max-width: 100%!important;
width: 100%!important;
}
#avia-menu .avia-menu-text {
font-size: 20px !important;
}