I am trying to override Muirawer-paper css , it applying in local after running “npm start”. But not applied when running build package.

.css-12i7wg6-MuiPaper-root-MuiDrawer-paper {
    position: absolute !important;
    top: 50px !important;
    outline: 0;
    left: 10px !important;
    max-width: 35px;
    padding-right: 35px !important;
    background: color-mix(in srgb, #D8D8D8, transparent 18%) !important;
}

My local application:

After running build package:

Why is my CSS not applying in the build package?

The CSS should be same in both locally and build package when running the react application.

Header.js

import * as React from 'react';
import { styled, useTheme } from '@mui/material/styles';
import Box from '@mui/material/Box';
import MuiDrawer from '@mui/material/Drawer';
import MuiAppBar from '@mui/material/AppBar';
import Toolbar from '@mui/material/Toolbar';
import List from '@mui/material/List';
import ListItem from '@mui/material/ListItem';
import ListItemButton from '@mui/material/ListItemButton';
import ListItemIcon from '@mui/material/ListItemIcon';
import ListItemText from '@mui/material/ListItemText';
import Tooltip from '@mui/material/Tooltip';
import HomeIcon from '@mui/icons-material/Home';
import LayersIcon from '@mui/icons-material/Layers';
import  './Header.css';
//comment 
const drawerWidth = 240;

const openedMixin = (theme) => ({
  width: drawerWidth,
  transition: theme.transitions.create('width', {
    easing: theme.transitions.easing.sharp,
    duration: theme.transitions.duration.enteringScreen,
  }),
  overflowX: 'hidden',
});

const closedMixin = (theme) => ({
  transition: theme.transitions.create('width', {
    easing: theme.transitions.easing.sharp,
    duration: theme.transitions.duration.leavingScreen,
  }),
  overflowX: 'hidden',
  width: `calc(${theme.spacing(7)} + 1px)`,
  [theme.breakpoints.up('sm')]: {
    width: `calc(${theme.spacing(8)} + 1px)`,
  },
});

const DrawerHeader = styled('div')(({ theme }) => ({
  display: 'flex',
  alignItems: 'center',
  justifyContent: 'flex-end',
  padding: theme.spacing(0, 1),
  // necessary for content to be below app bar
  ...theme.mixins.toolbar,
}));

const AppBar = styled(MuiAppBar, {
  shouldForwardProp: (prop) => prop !== 'open',
})(({ theme, open }) => ({
  zIndex: theme.zIndex.drawer + 1,
  transition: theme.transitions.create(['width', 'margin'], {
    easing: theme.transitions.easing.sharp,
    duration: theme.transitions.duration.leavingScreen,
  }),
  ...(open && {
    marginLeft: drawerWidth,
    width: `calc(100% - ${drawerWidth}px)`,
    transition: theme.transitions.create(['width', 'margin'], {
      easing: theme.transitions.easing.sharp,
      duration: theme.transitions.duration.enteringScreen,
    }),
  }),
}));

const Drawer = styled(MuiDrawer, { shouldForwardProp: (prop) => prop !== 'open' })(
  ({ theme, open }) => ({
    width: drawerWidth,
    flexShrink: 0,
    whiteSpace: 'nowrap',
    boxSizing: 'border-box',
    ...(open && {
      ...openedMixin(theme),
      '& .MuiDrawer-paper': openedMixin(theme),
    }),
    ...(!open && {
      ...closedMixin(theme),
      '& .MuiDrawer-paper': closedMixin(theme),
    }),
  }),
);

export default function MiniDrawer() {
  const theme = useTheme();
  const [open, setOpen] = React.useState(false);

  const handleDrawerOpen = (index) => {
    console.log("index",index)
    setOpen(true);
   
  };

  const handleDrawerClose = () => {
    setOpen(false);
  };

  return (
    <Box sx={{ display: 'flex' }}>
      
      <AppBar position="fixed" color="default" >
        <Toolbar variant="dense">
        </Toolbar>
      </AppBar>
    <Drawer variant="permanent" open={open} 
     sx={{
      "& MuiPaper-root.css-12i7wg6-MuiPaper-root-MuiDrawer-paper": {
        position: "absolute !important",
        minHeight: "fit-content !important",
        top: "50px !important",
         outline: 0, left: "10px !important", width: "35px", padding:" 35px !important", background: "color-mix(in srgb, #D8D8D8, transparent 18%) !important"
      }
    }}
    //  style ={{position: "absolute !important",top: "50px !important", outline: 0, left: "10px !important", width: "35px", padding:" 35px !important", background: "color-mix(in srgb, #D8D8D8, transparent 18%) !important"}}
    >
       
        <List>
          {[
            "Home",
            "Layers",
           
          ].map((text, index) => (
            <ListItem key={text} disablePadding sx={{ display: "block" }}>
              <ListItemButton
                sx={{
                  minHeight: 48,
                  justifyContent: open ? 'initial' : 'center',
                  px: 2.5,
                }}
              >
                <ListItemIcon
                  sx={{
                    minWidth: 0,
                    mr: open ? 3 : 'auto',
                    justifyContent: 'center',
                  }}
                >
                  <Tooltip title="Home">
                 {index === 0 ? <HomeIcon />:null} 
                 </Tooltip>
                 <Tooltip title="Layers">
                 {index === 1 ? <LayersIcon />:null} 
                 </Tooltip>
          
              
                </ListItemIcon>
                <ListItemText primary={text} sx={{ opacity: open ? 1 : 0 }} />
              </ListItemButton>
            </ListItem>
          ))}
        </List>
       
      
      </Drawer>
     
    </Box>
  );
}

Header.css

.css-12i7wg6-MuiPaper-root-MuiDrawer-paper{
    position: absolute !important;
    top: 50px !important;
    outline: 0;
    left: 10px !important;
    max-width: 35px;
    padding-right: 35px !important;
    background:color-mix(in srgb, #D8D8D8, transparent 18%) !important;
}

App.js:

import logo from './logo.svg';
import './App.css';
import Registration from './components/Registration';
import Header from './components/Header';


import Paper from '@mui/material/Paper';

function App() {
  return (
    <div className="App">
       
      <Header />
      
      <Paper className = 'footer'  sx={{ position: 'fixed', bottom: 0, left: 0, right: 0,backgroundColor:'rgba(217, 217, 217, 0.6)' }} elevation={3}>
        
      </Paper>

    </div>
      
    
  );
}

export default App;

App.css:

.App {
  text-align: center;
}

.App-logo {
  height: 40vmin;
  pointer-events: none;
}