Open 'overlay' form/window

I am in the early stages of evaluating the conversion of one of my MS Access databases to LibreOffice & am struggling with finding a way to open a modal, popup ‘overlay’ type window/form, as in screen shot attached. Basically, on pressing a button on the main parent window, I need a popup window to be shown, overlaying the parent one but without any type of border, min, max or close buttons.

A dialog would work perfectly, blocking access to the parent form until it is closed, except for always having a border & I have been unable to find a way to achieve the same with a standard form. Any advise as to how this may be achieved (ie. similar to setting the Access form property ‘Border Style’ to ‘None’)?

I have same probem…

In may case I want to show login window at startup.

Any idea?