#435 web dark mode (#455)

* add ThemeProvider to App.web.tsx

* make FlatNavigator use themed color

* fix extra padding on top in web

* add observer to App.web.tsx to make it react to theme changes

* fix TS for useColorSchemeStyle

* add dark mode toggle button to web LeftNav

* fix index.web.tsx border colors for web

* Move the darkmode desktop web toggle to the right nav column

---------

Co-authored-by: Paul Frazee <pfrazee@gmail.com>

src/view/screens/Home.tsx

@@ -1,5 +1,5 @@
 import React from 'react'
-import {FlatList, View} from 'react-native'
+import {FlatList, View, Platform} from 'react-native'
 import {useFocusEffect, useIsFocused} from '@react-navigation/native'
 import {observer} from 'mobx-react-lite'
 import useAppState from 'react-native-appstate-hook'
@@ -187,12 +187,11 @@ const FeedPage = observer(
           key="default"
           feed={feed}
           scrollElRef={scrollElRef}
-          style={s.hContentRegion}
           showPostFollowBtn
           onPressTryAgain={onPressTryAgain}
           onScroll={onMainScroll}
           renderEmptyState={renderEmptyState}
-          headerOffset={HEADER_OFFSET}
+          headerOffset={Platform.OS === 'web' ? 0 : HEADER_OFFSET} // only offset on mobile
         />
         {feed.hasNewLatest && !feed.isRefreshing && (
           <LoadLatestBtn onPress={onPressLoadLatest} label="posts" />