Settings->Screen options->Show toolbar->Vertical
is selected. By default, the number of toolbars columns shown on the right-side screen will match the number of toolbars defined.
The toolbar buttons will be distributed from left to right from the top and down, so that the Toolbar 1 buttons will start on the first row and continue of the next row(s), then the Toolbar 2 buttons will follow on the next rows and so on.
Settings->Toolbar setup->Vertical toolbar
. And the number toolbar columns shown on the right side of the screen can be less than the vertical toolbar columns number enabling horizontal toolbar scrolling.
The number of columns shown is by default equal the number of Vertical toolbar columns. If the visual number is less, horizonal toolbar scrolling shows hidden columns. If the number is larger, the default value is used.