Resize a pane in a tool window by using the mouse to grab its border with another pane, called a splitter, and dragging the border to a new location. To control how panes are resized when you resize the window, select the splitter
               and choose one of the following in the right-click menu: 
            
            
            
               
               - For a vertical splitter, Keep First preserves the size of the panes to the left of the splitter. For a horizontal splitter, Keep First preserves the size of the panes above the splitter.
               
- For a vertical splitter, Keep Second preserves the size of the panes to the right of the splitter. For a horizontal splitter, Keep Second preserves the size of the panes below the splitter.
               
- Keep Proportion preserves the length and width ratio of the panes on either side of the splitter.