Please help me change background color on a post

Can you please tell me how to change the background to white on this post without affecting the other colors on the site? I am using twenty fourteen template.
https://www.getalifemedia.com/mobile/contact/

I have tried this and it does not work:

.postid-498 .hentry {
background-color: #ffffff !important;
}

and this does not work either

.postid-498 {
background-color: #ffffff !important;
}

Any help would be appreciated! Thanks!