Our website builder has a cool feature where you can customize the sections of your site for different size screens. Select the element you want to resize then go to Screen Options and check the box that corresponds to the device you want to optimize for. For example, if it looks fine on desktop and tablet but not mobile then check "Hide on extra small screens".

Now, duplicate the element and edit it however you want to look good on that device. Then go into the screen options and check the boxes to hide it on the other devices. For example, if you're optimize this element for mobile then check the boxes corresponding to desktop and tablets.