Add dark mode (#199)

* Add passive dark mode to everything but codemirror

* Add dark theme support for Codemirror

* Make theme a user setting

* Fix button text size

* guard against undefined window

* Formatting and test fix

src/components/Toolbar/SetAbsDistance.tsx

@@ -131,9 +131,6 @@ export const SetAbsDistance = ({
           console.log('e', e)
         }
       }}
-      className={`border m-1 px-1 rounded text-xs ${
-        enableAngLen ? 'bg-gray-50 text-gray-800' : 'bg-gray-200 text-gray-400'
-      }`}
       disabled={!enableAngLen}
     >
       {buttonType}