You can add a shadow effect for structure or stripe, just notice that the shadow will not appear in all browsers.
If you want to add this type of shadow:
you need to:
click on the needed structure or stripe and open the code-editor;
and add styles for box-shadow: rgb (236, 236, 236) 1px 1px 3px;
Besides you can also try to find any CSS generator for shadow, choose suitable variants and add to the CSS styles tab for this stripe.
Here you can check which email clients support the shadow effect - https://www.caniemail.com/search/?s=shadow