F12 to open inspect window.
In the Console tab enter:

viewer.style = 'filter: grayscale(1) invert(1)'

Or

viewer.style = 'filter: grayscale(1) invert(1) sepia(1)'

Or create a bookmark and put this in it

javascript:(function(){document.body.parentElement.style = 'filter: grayscale(1) invert(1) contrast(0.8)';})()
Then use the bookmark when viewing the pdf.