I wish to add shading to my chart between two values on my Y axis.

[#1]

I wish to add shading
to my chart between two values on my Y axis.

(I am using a box
plot with three dimensions and an expression for the data values).

So far I can only use
reference lines of 10pt width and need multiples to shade the area. Also if I
zoom in these do not scale and I am left with a horizontally stripped chart.
Has anyone a solution for this please ?

[#2]

Is there a way to increase the line width above 10pt ? Can this value then be set via an expression ?

[#3]

The solution for Shading Graph Gap - Gross Margin works OK for a Line graph but not for a box plot. Can anyone suggest a way forward with this ?