When a control is docked to an edge of its container, it is always positioned flush against that edge when the container is resized. If more than one control is docked to an edge, the controls appear side by side according to their z-order; controls higher in the z-order are positioned farther from the container's edge.
If DockStyle.Left, DockStyle.Right, DockStyle.Top, or DockStyle.Bottom is selected, the specified and opposite edges of the control are resized to the size of the containing control's corresponding edges. If DockStyle.Fill is selected, all four sides of the control are resized to match the containing control's edges.