Changing button color for embeded element with CSS

Site URL: https://6thdimensionvr.com/gamelist-demo

Hi all!

I have an HTML embed code for my website that shows game options for my arcade. I can't edit the HTML code without breaking it, so I'm trying to edit the color and shape of the dropdown buttons in the custom CSS. 
But I need a way to only alter the button color for this specific element, and I am not sure where to begin.

I appreciate the help. 

The embed looks like:

<div id="loadSvrGamesWidget"></div> 

<script> 

    var svrScript = document.createElement('script'); 

    svrScript.onload = function () { 

        window.svrLoadGames({ 

            skipVariants: true, 

            groupByCategories: "*" , 

            container: '#loadSvrGamesWidget', 

            rowSize: '200%', 

            uuid: 'd0bb98c0-23d0-5761-bd00-2fc70c374b7c', 

            gamesPerRow: 3

         
        }); 

    }; 

    svrScript.src = '//api.synthesisvr.com/javascripts/WordpressWidget.js'; 

    document.head.appendChild(svrScript); 

</script> 
<div>

<div> <center>
  Search: <input type="text" onkeyup="window.svrSearchTitle(this.value);"></div>
 

Change all these buttons?