Customising DearFlip button bar with css

I want to customise the color and size of the buttons below my FlipBook in the “Press” section.

I’ve added various versions of the following to the custom css of Elementor, but nothing is doing what I want it to do – and have done using ‘inspect’ in a browser, which has always worked for me in the past (screenshots available: looks great, and doesn’t overpower the thumb). I’m obviously using the wrong syntax, but struggling to find anything consistent to show what

.df-ui {
height: 55px;
}

.df-ui-page {
font-size: 11px;
line-height: 17px;
}

.df-ui.btn {
colour: #ccc;
width: 18px;
font-size: 15px;
background-color: #000;
height: 50%;
line-height: 1;
padding: 0,0;
}

The page I need help with: [log in to see the link]