calendar formatting issue

Hi

I have a couple of sites that both use the get_calendar function and have the same problem. The most noticible site is at https://www.teejayuu.co.uk. when viewing from the home page everything looks normal, it shows the previous nav button in the bottom left. If click the link the column under Thursday widens to display the Next link. I am using the Slimple theme on this site and thegreenmountain on the other. I have tried allsorts of formatting in css to no avail. I think this maybe a problem with the get_calendar function itself, but don’t feel competant to understand or have the desire to change the ‘guts’ of the software. If anyone can point me in the right direction I would appreciate it.