Fixed using the following CSS:
/*SEARCH FORM IN MENU*/
#searchform>div {
max-width: 600px !important;
display: inline-block !important;
opacity: 100 !important;
}
.avia_mobile #top #searchsubmit, .avia_mobile .ajax_load {
height: 39px;
}

but the issue I’m having is that the resulting does not allow users to click on that link.