Just wanted to make sure that I am correctly understanding what you would like to do. You are trying to change the currently shown background and change it with the pure white background, through out all of the steps?
If so, can you please tell us which theme you are using?
It is often with CSS good to know the URL to the player or recorder in this case so that we can check it out and see any specific code that might be needed. This helps in cases where other codes are making it harder for changes to be applied - like you being required to be using !important; in the rules.