How to make a split screen stack on mobile

Site URL: https://stingray-calliope-krgc.squarespace.com/

Hi! I created a split screen banner and I can't make the elements stack for the mobile version. Now they look squished one next to each other, and I would like to be the next first and the image below.

This is the page: https://stingray-calliope-krgc.squarespace.com/

To split the banner I used this code: 

[data-section-id="6140af52a4ed9f625b7f25ec"]{
.section-background{
  width:50%;
  margin-left:50%;
}
.content-wrapper{
  width:50%;
  margin-right:50%!important;
}}

Would really appreciate some assistance with this 🙂 

Hi,

What is password?