Hi,
It’s because of this theme CSS rule, it makes it invisible with 0 opacity:
[html].cactus-header-search-form form {visibility: hidden; opacity: 0; position: absolute;top: 0;left: 0;bottom: 0;right: 0;background-color:rgba(38,38,38,1.0);transition: all 0.2s ease-in-out;-webkit-transition:all 0.2s ease-in-out;}[/html]
Try adding this rule:
[html].probox .proinput form {
opacity: 1 !important;
display: block;
visibility: visible;
background: transparent !important;
}[/html]