Improve dark mode css and contrast

webclient/src/App.js

@@ -2,6 +2,7 @@ import React, { useState, useEffect, useReducer, useContext } from 'react';
 import { BrowserRouter as Router, Switch, Route, Link, useParams, useHistory } from 'react-router-dom';
 import './semantic-ui/semantic.min.css';
 import './light.css';
+import './dark.css';
 import { Container, Divider, Dropdown, Form, Grid, Header, Icon, Image, Menu, Message, Segment, Table } from 'semantic-ui-react';
 import Darkmode from 'darkmode-js';
 import { isAdmin, requester } from './utils.js';