In the Database Preferences you can specify the name of a custom CSS file to load.  This would be the best place to place all of the CSS updates for that database.  You can also point this to a single corporate CSS style for consistency.
Database Preferences
In this CSS file you can add the following to make the background of all Form Areas white.
.detailFields {
    background-color: white;
    border-radius: 5px;
}