Update chosen.scss for chrome gripe fix

Fixes this chrome gripe:
Consider using 'dppx' units, as in CSS 'dpi' means dots-per-CSS-inch, not dots-per-physical-inch, so does not correspond to the actual 'dpi' of a screen. In media query expression: only screen and (-webkit-min-device-pixel-ratio: 2), only screen and (min-resolution: 144dpi)