How can I make this scroll area a wider so I can aim at it a better with my mouse cursor?
Here's something else I've discovered about "aiming" at the scrollbar that might be helpful. If you you have your browser window maximized, you can just move your mouse all the way to the right edge of the screen, even to the point where the mouse pointer disappears off the edge of the screen, and go ahead and use the mouse wheel to scroll or, if you moved the pointer over the scrollbar slider, you can press the left mouse button and drag the slider. In other words, you don't need to actually see the mouse pointer in plain view.
And, if you want to drag the slider, once you've started dragging, you don't have to keep the mouse pointer on top of the slider. If the mouse pointer veers off the scrollbar, the mouse pointer will continue to hold the slider. In my browser window on my laptop, I can be dragging a slider and, even if I let the mouse pointer drift an inch or so to the left, it still controls the slider. If I left the mouse pointer drift farther away, it loses it's grip on the slider. Note: the actual distance the pointer can drift away from the slider and still remain in control of it probably depends on monitor resolution setting.