@Rizwan94 said: I tried creating a vertical layout with title widget and toolbar, and added that layout above central widget. That's close, but you need one extra step. Create a plain QWidget, set a vertical layout on it, add your widget and toolbar to it and then use setMenuWidget() on your main window. EDIT: Or you can even make it simpler - just use your title widget directly as the menu bar.

@SGaist That's a fair question and to answer that it's because on the actual dock widget itself, in the production code, there are two widgets that get placed inside the dock widget itself. The topFrame contains the layout for the QTabWidget as you have pointed out. The code that is not present, botFrame contains another QGridLayout. These two then get placed inside the QGridLayout which is the layout of QGroupBox. Then to answer Why am I subclassing a layout to put widgets in it? I guess this is a personal decision and can be argued either way. For now, I will say that you are correct, that the Widget should manage the way the GridLayout adds widgets to them. However, I will argue that since QGridLayout is it's own class; the Widget does not "own" the widgets, rather, the layout owns the widgets since QWidget does not have a addWidgets function in it. Therefore, QGridLayout owns and is responsible for the Widgets that it owns. Hence the decision that the QWidget is the parent, which has a QGridLayout, which the QGridLayout as the Child, has the widgets that belong inside of it. This is a programming decision that I made with these arguments.

@J.Hilk said in Set fixed margin/spacing/padding between Widgets/Layouts: @wrekler you have to set the margin and spacing of the QLayout item to 0 as well, not only in the StyleSheet. I believe those are 2 different pairs of shoes. @JonB said in Set fixed margin/spacing/padding between Widgets/Layouts: To clarify what @J-Hilk is saying (which I believe to be correct): a QLayout is not a QWidget and so cannot have its attributes affected via a stylesheet rule (sadly). That has to be done via explicit, back-end code. Here we go! That was the problem! Layout cannot be affected by a stylesheet file! Now I know how styling layout works! Thank!

@MCam Thank you, I was using plain adjustSize() that's why it didn't resize. Although there is problem that remains even when resizing both layouts : After unmaximising the window, adjustSize gives this result. I will mark the thread as solved because I can make the window to not be able to get maximized, but for completeness shake it would be nice if this result could be avoided. Either way, you saved my day and I thank you very much for that :)

I have posted suggestion about adding such positioner to QtQuick: https://bugreports.qt.io/browse/QTBUG-57549

@vladstelmahovsky Thanks. This solves the issue! Shame on me for not reading the documentation more thoroughly.