custom menu drop down in ie

I am building a theme for a new site and have a problem in ie.
the drop down menu does not work. I am using a custom menu.
it is fine in firefox and chrome.
I have not touched the html it is exactly as wp intended.
I have made minor alterations to css background color.
If anyone can spot the problem please let me know.
Thankyou in advance
Paul

Here is my address
https://www.perfectportugalproperty.co.uk/portugal/

and here is my css

[CSS moderated as per the Forum Rules. Please just post a link to your site.]