Search Form Not Mobile Friendly

Hi Everyone, I am totally new to this, but seem to have everything else working fine except one vital issue, the search form does not seem to be mobile friendly. When viewed on a mobile, the form overflows, creating a horizontal scroll bar, i’m assuming the fix is simple, but cannot work out how to make the search form be mobile friendly, can anyone help please?

ps, i have added css the hide the overflow, this just cuts the search form off.

Thank you in advance… ??

The page I need help with: [log in to see the link]