Restoring a Split Window
The procedure to merge a split window back into a single window is similar to the procedure used to split it in the first place.
Click on a tab in the editor and drag it away from the top of the editor window. You should see a red outline appear in the window that moves depending on where you move the mouse while dragging the tab.
The red outline indicates where the tab will snap into place when you release the mouse button. Drag the tab to the top of the window until the red outline appears as a box along the top with the tab's outline in the tab bar, then release the mouse and the tab should pop into place in the same position within the row of tabs as its outline indicated. If you don't see the tab's outline as part of the box at the top of the window and you release the mouse, you will simply split the window vertically.