Vaadin Framework version: 8, all versions

There is a major error in the class com.vaadin.server.VaadinSession (and possibly other classes too, if this is some kind of cargo cult programming in the Vaadin team)

Most public methods in the class use assertions to "check" if the session has the lock. This is fundamentally wrong. Assertions are the wrong tool to check preconditions in public meth

Description

Grid with item details opened- after item deleting and grid refreshing the attribute 'details-opened' stays in a row, that is, in the item that was below the deleted one, even if I call setDetailsVisible(item, false) before deleting an item and doing refreshAll() on the grid.

I add a style for grid row which has item details opened to show what I'm talking about:

#items [

Since #8506 has been fixed, a Registration is supposed to be idempotent (or idempotent-ish at least), i.e. calling remove() multiple times has the same effect as calling it once.

However, this is not mentioned explicitely in the documentation:

https://github.com/vaadin/flow/blob/c009afc5c24d8a3d6abc14f6f5cd3faea80c1932/

Describe the bug

The create account page is not responsive.

To Reproduce
Steps to reproduce the behaviour:

1. Go to localhost:3000/sign-up
2. See error

Expected behaviour

Everything should be centred in the middle of the page, even for mobile devices.

Screenshots

At 2560x1440p:
![image](https://user-images.githubusercontent.com/11173328/109273971-ce3c5a80-7