Changing hover color for Back button in Simple Layout

I have a survey with the Simple Layout, and some custom CSS for the Back/ Next buttons. 

The problem is that while hovering with the mouse over “Next’ turns te background to my primary color, hovering over “Back’ makes it light gray. I think this is the standard for that layout.

How can I override the hover background color of the Back button?

This is what I have right now:

/* next button */
#navigation #next-button {
    background-color: #BEBEBE;
    color: #192743;
    font-weight: bold;
    font-size: 13px;
    width: 100px;
    margin-left: auto;
}

/* previous button */
#navigation #previous-button {
    background-color: #BEBEBE;
    color: #192743;
    font-weight: bold;
    font-size: 13px;
    width: 120px;
    margin-right: auto;
    border: none;
}