Need Help for navigation css

hello members

i am working in horizontal menu

i have css problem like

when i place the mouse cursor on the parent category menu work fine

but when i place the cursor on the sub-category (drop down) background (white color) disappear on the parent category , looking for help

here is the link

http://bit.ly/bbm3qc+

try pointing on horizontal menu sports

and sub menu (drop down )

Thank you