There are styles in caspian css :-
.controls-pane .toggle-button {
    -fx-background-radius: 4, 4, 3, 2;
    -fx-padding: 3 6 3 6;
}

controls-pane is too generic, needs to be more specific :
.custom-color-dialog .controls-pane .toggle-button { ... }

The above defines the hierarchy more specifically.