The 2.8 documentation
doesn't seem to have been updated yet to the new type of sliders that have a split function,
top half (upward pointing single headed arrow for coarse control) and bottom half (sideways pointing double headed arrow for fine control), with the mouse pointer.
Having now got used to it, i find using the mouse works quite well too provided the size slider itself is
not sized too small by making the dock/dialogue too narrow and also provided the size slider is fairly
central on the screen i.e not on a dock at the edge of the screen as that restricts the bottom half function of the slider.