[Snackbar] Add support for CSS variables (#32603)

docs/pages/experiments/material-ui/snackbar.tsx

@@ -0,0 +1,91 @@
+import * as React from 'react';
+import {
+  Experimental_CssVarsProvider as CssVarsProvider,
+  useColorScheme,
+} from '@mui/material/styles';
+import CssBaseline from '@mui/material/CssBaseline';
+import Box from '@mui/material/Box';
+import Container from '@mui/material/Container';
+import Moon from '@mui/icons-material/DarkMode';
+import Sun from '@mui/icons-material/LightMode';
+import Button from '@mui/material/Button';
+import Snackbar from '@mui/material/Snackbar';
+import MuiAlert, { AlertProps } from '@mui/material/Alert';
+
+const Alert = React.forwardRef<HTMLDivElement, AlertProps>(function Alert(props, ref) {
+  return <MuiAlert elevation={6} ref={ref} variant="filled" {...props} />;
+});
+
+const ColorSchemePicker = () => {
+  const { mode, setMode } = useColorScheme();
+  const [mounted, setMounted] = React.useState(false);
+  React.useEffect(() => {
+    setMounted(true);
+  }, []);
+  if (!mounted) {
+    return null;
+  }
+
+  return (
+    <Button
+      variant="outlined"
+      onClick={() => {
+        if (mode === 'light') {
+          setMode('dark');
+        } else {
+          setMode('light');
+        }
+      }}
+    >
+      {mode === 'light' ? <Moon /> : <Sun />}
+    </Button>
+  );
+};
+
+export default function SnackbarCssVars() {
+  const [open, setOpen] = React.useState(false);
+  const handleClick = () => {
+    setOpen(true);
+  };
+
+  const handleClose = (event?: React.SyntheticEvent | Event, reason?: string) => {
+    if (reason === 'clickaway') {
+      return;
+    }
+
+    setOpen(false);
+  };
+
+  return (
+    <CssVarsProvider>
+      <CssBaseline />
+      <Container sx={{ my: 5 }}>
+        <Box sx={{ pb: 2 }}>
+          <ColorSchemePicker />
+        </Box>
+        <Box
+          sx={{
+            display: 'grid',
+            gridTemplateColumns: 'repeat(auto-fill, minmax(256px, 1fr))',
+            gridAutoRows: 'minmax(160px, auto)',
+            gap: 2,
+            '& > div': {
+              placeSelf: 'center',
+            },
+          }}
+        >
+          <Box>
+            <Button variant="outlined" onClick={handleClick}>
+              Open success snackbar
+            </Button>
+            <Snackbar open={open} autoHideDuration={6000} onClose={handleClose}>
+              <Alert onClose={handleClose} severity="success" sx={{ width: '100%' }}>
+                This is a success message!
+              </Alert>
+            </Snackbar>
+          </Box>
+        </Box>
+      </Container>
+    </CssVarsProvider>
+  );
+}

packages/mui-material/src/Snackbar/Snackbar.js

@@ -55,7 +55,7 @@ const SnackbarRoot = styled('div', {
   };
 
   return {
-    zIndex: theme.zIndex.snackbar,
+    zIndex: (theme.vars || theme).zIndex.snackbar,
     position: 'fixed',
     display: 'flex',
     left: 8,