Table and cell borders
 
The rightmost eight toolbuttons of the Table toolbar determine whether the borders of the cells selected are visible or hidden. Click any cell and see which of these border toolbuttons are depressed. Clicking any of them again reverses their effect.
 
Fig. 1: Original
Cell 1 Cell 2
Cell 3 Cell 4
This is the original table.
 
 
Fig.2: Hide borders
Cell 1 Cell 2
Cell 3 Cell 4
This can be reversed by clicking Show borders1.
 
Fig.3: Show outer border(s)
Cell 1 Cell 2
Cell 3 Cell 4
This can can be reversed by clicking Show inner border(s)
 
Fig.4: Hide borders then Show inner border(s)
Cell 1 Cell 2
Cell 3 Cell 4
This can be reversed by clicking Show borders.
 
Fig.5: Show left border and Show right border disabled in all cells
Cell 1 Cell 2
Cell 3 Cell 4
 
Fig.6: Show top border enabled in lower cells and Show bottom border enabled in upper cells.
Cell 1 Cell 2
Cell 3 Cell 4
Combining these borders results in a thicker line which makes a convenient divider.
 
Fig.7: Show top border disabled in lower cells and Show bottom border disabled in upper cells.
Cell 1 Cell 2
Cell 3 Cell 4
 
Fig.8: Show right border enabled in Cell 1 and Show left border enabled in Cell 2. Show right border disabled in Cell 1 and Show left border enabled in Cell 4.
Cell 1 Cell 2
Cell 3 Cell 4
Cells 3 and 4 display the standard configuration as seen in Fig. 1. You would expect that adding Cell 1's right border would cause a thicker partition, but its only effect is to stagger the existing one towards Cell 1. The only remedy is to disable Cell 1's right border.
 

 
Notes:
  1. If you highlight a block of text and accidentally click any of the Show ... border toolbuttons your paragraph will display a horizontal or vertical line along one of its borders like part of a table. Doing this deliberately is not recommended as such stray table cell wall lines may cause interference with text and prove difficult to remove.