How are Grid Lines established?

Grid lines are created when you define tracks in the explicit grid using CSS Grid Layout. In the following example there is a grid with three column tracks and two row tracks. This gives us 4 column lines and 3 row lines. Lines can be addressed using their line number.

7.03-1.70=5.33 and 6.80+5.09=11.89 and 5.5-3.01=2.49