added default-only styles

here are the default styles. i'm pretty sure this is a good way to handle css for components like this, or at least the best way we have with what css gives us. the basic idea is that you only add styles that are required to make the component function like normal.

for example, the disabled `pointer-events` style isn't something the user is going to assume they need to add, and that's inherent to whether `select` works or not, so it's added. and `display: inline-block` is there since it makes the select act like a native input type right out of the box. it's slightly closer to theme, but it's a "sensible default" so it fits the bill.

and then the user expects to add styles purely for themeing, like `border-radius`, `background-color` etc.

also i like to add a comment to the top of the files showing the dom structure to expect