I have a problem with my website with mobile device

Hello,

I have a problem with my website with mobile device
on mobile screen, section overlap but I don t understant why because works well with classic device and don t have special rule for mobile device

I have tried with firebug to find where is my problem bu don t know.

I have a class for each section of site (corresponding to a row with bachground white or blue)

Could you help me?

here is the picture