refactor more hooks

hooks/useTheme.ts

@@ -0,0 +1,15 @@
+import { useContext } from "react";
+import { ThemeContext } from "../contexts/ThemeContext";
+
+// convenience hook to get access to ThemeContext's state/functions from pages/components/etc.
+const useTheme = () => {
+  const context = useContext(ThemeContext);
+
+  if (!context) {
+    throw new Error("useTheme must be used inside of a ThemeProvider.");
+  }
+
+  return context;
+};
+
+export default useTheme;