position:sticky not working

The registration box in the page crossing35.com/investors/ should be sticky so that it's in the window when you scroll. The page is created using OptimizePress LiveEditor. The class fixed-reg is in the settings for the optin element. The CSS is in the page settings menu on the right.

I've tried it a number of ways and the CSS may be disabled after testing. position:fixed works OK except for at the bottom, where it crashes the footer.

Sticky should rise until a predefined distance from the top but doesn't. As suggested with examples online, I've tried to change the overflow setting in the container but that had no effect. Support access is enabled.

Any suggestions?