Adding Custom Code for desktop and mobile

Site URL: https://unitydesignsummit2022.squarespace.com/

Hi the current video on the desktop as it is not responsive and I would like to know how to leave this on on desktop and have an alternative for mobile. Thank. What is the code. 

It looks like you solved with this code to Page Header?

<style>
@media only screen and (max-width: 780px) {
    #page section:nth-of-type(1) { 
            display: none; 
    } 
  }
@media only screen and (min-width: 600px) {  
    #page section:nth-of-type(2) { 
        display: none !important;
    }
  }
</style>