Dave,
The css of the apply/cancel filter buttons are controlled by the primary button properties in the theme editor. Unfortunately, that means that if you change those properties for the apply/cancel it will potentially apply to other buttons on your page as well, which you may or may not want. Another option is to use custom CSS. Check out this general tutorial about custom CSS. You can add a css class to the table under Display->Advanced, and then use the chrome console to get the element class name of the buttons to change their properties. An example would be:
.tableClass .nx-header-right .ui-button {
Background: black; this changes the background color of the apply/cancel buttons
Color: gray; this changes the color of the button text
border:1px solid black; this controls the shadow property (visible in the theme editor)
}
I can’t guarantee this custom CSS will always work, but it should point you in the right direction.
Thanks!
Amy