Please note!
Custom positioning is not considered best practice for responsive web design and should not be used too frequently.
selector {color: red;}
// For main element
selector .child-element {margin: 10px;}
// For child element
.my-class {text-align: center;}
// Or use any custom selector
Unfortunately, this feature is not available in the demo. You should see it after installing the app into your store.
Or you can take a look on the video below to see how it works in action.