A scroll bar is a rectangle that contains a scroll box and has direction arrows at both ends. The user can tap the arrows, click on the gray area between the arrows, or drag the scroll box to scroll the scroll bar's parent window.
Scroll bar
Scroll bars should be included in any window for which the content of the client area extends beyond the window's borders. A scroll bar's orientation determines the direction in which scrolling occurs when the user operates the scroll bar. A horizontal scroll bar enables the user to scroll the content of a window to the left or right. A vertical scroll bar enables the user to scroll the content up or down.
You can use as many scroll bar controls as needed in a single window. When you create a scroll bar control, you must specify the scroll bar's size and position. However, if a scroll bar control's window can be resized, your application must adjust the scroll bar's size whenever the size of the window changes.