Hidden elements with in menu and border

Hello, I would like to make a menu with hidden elements. My problem is: I never know how to stretch border or rectangle which is behind this elements. For example we have a menu like this :

When we click on the button inside we have more elements like this :

Here is the full link to this page ( menu is on the left )

My question is , how to make it ? Thank you for answers

You can use toggle for this or use simple hide and show. but create 2 list one with the half content and the other with full content.

When user click on the button then hide the first content and show the second content.

Thank you for your answer but I think this shouldn’t work on this menu because I have a lot of elements which sizes are different. For example one hiden element is quite bigger than other ones, I mean this just don’t fit. Check this out

Okay, you need to set widget border to things like hidden, transparent, and also use push and pull

Work around it you are nearly there