vertical sliders

Hi @danielstern!

love your tool and helped me greatly on my current project.

However for the app i'm building i discovered that on android i have a little issue, when my slider is set to be vertical.

`writing-mode: bt-lr;
-webkit-appearance: slider-verticalt;`

is the css i used to make it vertical, however then your css doesnt work anymore as it seems to overwrite the appearance.

I used a weird, hacky way with transform to rotate the slider, but ran into issues with the transform origin and the sizes and had to make the position absolute for now. However i'd like to revert the absolute positioning and set the height and width to their actual values, so other elements see them as such.

could you have a look?