There’s no way to do that, no. The widgets get auto-sized based on the length of the text within.
In high-DPI set-ups you shouldn’t need to set different ‘pixel’ values for the widgets: In HTML and CSS ‘px’ units are not physical units, the browser translates ‘2px’ into the appropraite number of physical display pixels based on the DPI setting (so, on a regular display 2px is 2 display pixels, but on a retina display it’s 4px.)
It is not the case (outside of the 2D APIs of the
API) that you ever have to worry about the HiDPI translation yourself.
Given that, can you give a little more information about what you’re building that’s requiring manual sizing? In some browsers you can also use the CSS zoom property to blow up UI if you’re trying to make something intentionally oversized, although I don’t know how that then interacts with the HiDPI measurements.