Welcome to Webflow! This is because you have set your ‘Hero Section’ element to 30Vh. It will maintain this height, no matter what is in it. I would recommend:
Select the Hero Section element and remove it’s height property.
Select the yellow ‘Hero Section’ ‘Main’ element and set it’s top and bottom padding to 100px (or your desired effect).
Drag in your next section element underneath and it will work!
Here’s an update. I tried it and it works, but with the padding set to 100 pix on top it appears fine on the designer. When I view it in the browser mode, there’s a gap between the main yellow hero section and the one below.