Implement dark mode

Resolves #206

web/src/components/styles.js

@@ -1,19 +1,18 @@
 import { Typography, Container, Backdrop, styled } from "@mui/material";
-import theme from "./theme";
 
 export const Paragraph = styled(Typography)({
   paddingTop: 8,
   paddingBottom: 8,
 });
 
-export const VerticallyCenteredContainer = styled(Container)({
+export const VerticallyCenteredContainer = styled(Container)(({ theme }) => ({
   display: "flex",
   flexGrow: 1,
   flexDirection: "column",
   justifyContent: "center",
   alignContent: "center",
   color: theme.palette.text.primary,
-});
+}));
 
 export const LightboxBackdrop = styled(Backdrop)({
   backgroundColor: "rgba(0, 0, 0, 0.8)", // was: 0.5