Is it possible to turn off these separators(on the screenshot)?
Is it possible to modify them?
I found how to turn off horizontal borders.
What I want to know now- is it possible to modify the look of the vertical separators?
Dragging a button in a Toolbar slightly to the right adds a separator on the left-hand side of the button to “begin a group”. Similarly, the group separator can be removed by dragging the button slightly to the left. OR:
Right click the toolbar -> Customize -> right click the button -> Deselect 'Begin a Group':
It's not possible to modify the look of the vertical separators. But you could create your own separator,
save it as a .png file and create a new button with the .png file as button-image. 