The design choice of having a vibrant blue on top of a slightly different vibrant blue at the header of the site and questions is very jarring and difficult to look at. As someone who spends a lot of time on StackExchange this is by far the worst and most jarring design choice I have seen and made me not want to stick around.
It seems that most of it is coming from the white text on the bright blue, maybe it is also the font choice? Typically when white text is used in Material Design is is a heavier weight font (yes I know Roboto was used here) and is used sparingly if at all on light vibrant backgrounds.
A slightly more subdued pair of blues, taken directly from the Material Design Guidelines works much better and is less straining.
Something like this with #1976D2 for the upper background and #2196F3 for the question header strip: