Change background for lines in function/sub

[FutureCow]

I'd love to be easily able to see on the screen which lines are part of a function / subroutine and which aren't. As you can't cold fold, colouring them would make my life a lot simpler.

I tried changing the colour of the "whitespace" as opposed to the colour of the "background" but it colours the background of parts of lines rather than the background of full lines.

The end result of what I'm after would also be achieved if you could get the 1 pixel coloured line that marks the end of a function or subroutine and make that say 2 lines of text thick.
See the screenshot, hopefully that will make it easier to understand (the dark and light blue colourings are what I'd like to be able to replicate)

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