fix build and refactor from CR

explorer/src/api/constants.ts

@@ -1,7 +1,7 @@
 // master APIs
 export const API_BASE_URL = process.env.EXPLORER_API_URL;
 export const VALIDATOR_API_BASE_URL = process.env.VALIDATOR_API_URL;
-export const VALIDATOR_URL = process.env.VALIDATOR_URL;
+export const { VALIDATOR_URL } = process.env;
 export const BIG_DIPPER = process.env.BIG_DIPPER_URL;
 
 // specific API routes

nym-wallet/src/components/StyledBackButton.tsx

@@ -3,7 +3,7 @@ import { Button, SxProps } from '@mui/material';
 import ArrowBackIosNewIcon from '@mui/icons-material/ArrowBackIosNew';
 
 export const StyledBackButton = ({ onBack, sx }: { onBack: () => void; sx?: SxProps }) => (
-  <Button disableFocusRipple size="large" variant="outlined" onClick={onBack} sx={{ ...sx }}>
+  <Button disableFocusRipple size="large" variant="outlined" onClick={onBack} sx={sx}>
     <ArrowBackIosNewIcon fontSize="small" />
   </Button>
 );