Are you on a free plan? If so, your custom code will not work in the page header. If that’s the case, try using an HTML element placed somewhere on the page.
There’s no actual need for CSS styles to achieve this, since the new responsive engine does this for you. I get this behavior when the debugger is on, try turning the debugger off by changing the “debugger=true” to “debugger= false” in the URL parameter, remove the Style tag from the header, the configuration you have on the vertical behavior should be enough.
Could you share me the editor link (through DM) so I can have a look at it?
In Settings - General - Privacy, set the app to “everyone can view” on the “define who can see and modify the app”.
This would be the faster way to help you debug this.
If you don’t feel like letting anyone into the editor, then share with us the “group structure” on the element tree, there must be some parent group limiting the vertical stretch.