[css-grid] Far too much going on in section 1.4

Hello!

Section 1.2 and 1.3 are focused on a single topic of how to arrange grid-items using grid-area naming, grid-template-rows, grid-row, grid-template-columns, and grid-columns. They’re both straight forward and easy to understand. Section 1.4 however tries to tackle two features at once: the ability to stack items using z-index without absolute positioning and in the example the ability to utilize grid-line naming. It would be much less overwhelming if the grid-line syntax was placed into its own section similar to sections 1.2 and 1.3. Not to mention, it then be a great lead into the idea of z-index stacking. I understand this section is an overview, but this portion is putting brevity before clarity.


Thanks!
-- 
Malika Butler