Use MUI, structure change, fix API

frontend/components/Navbar.js

@@ -0,0 +1,25 @@
+import AppBar from '@mui/material/AppBar';
+import Box from '@mui/material/Box';
+import Toolbar from '@mui/material/Toolbar';
+import Typography from '@mui/material/Typography';
+import Place from '@mui/icons-material/Place';
+import Container from '@mui/material/Container';
+
+function Component() {
+  return (
+    <Box sx={{ flexGrow: 1 }}>
+      <AppBar position="static">
+        <Container>
+          <Toolbar>
+            <Place sx={{ marginRight: ".5rem" }} />
+            <Typography variant="h6" component="div" sx={{ flexGrow: 1 }}>
+              Chercher un code postal en Suisse
+            </Typography>
+          </Toolbar>
+        </Container>
+      </AppBar>
+    </Box>
+  );
+}
+
+export default Component;