Change background color on page And Show It (JAVASCRIPT)

Hello, I simply need to change a background color in the image I attached. What is circled in red, all that is grey in the background I want it changed to white. The files are .jsp so you must have knowledge in it. Once you are able to change it, I need to know where the file is located in the case I want to change the background color again. I am not sure where the exact file is located to change that background on the page, but i can direct you to the files where the css and etc is located This is a simple job and should not take long and need it to be done right now any questions please feel free to ask thankyou