I've never met a designer who wasn't completely fine with my suggestions for more pragmatic solutions. Like just styling a default scrollbar instead of implementing my own scrollbar to make it exactly like the design. Using a default drop-down menu instead of rolling my own just so I can round the corners of the selects.

The designers I've worked with are fine with these things. We have more important things to work on than small style details. We can go back and change these things later if anyone actually cares, but generally nobody ever does.