Can't justify content of grid ( Material-ui, React), Do you know how to fix?

I’m developing a site with React, but I can’t justify the grid items. As you can see I also created the "divcard" class for the initial . I tried different ways, but nothing works. I attach the grid code, and the divcard class. The grid code I attached is not complete. Thanks for the help

divcard: {

          backgroundColor: '#212121',
          padding: theme.spacing(3),
          flexGrow : 1,
          flex : 1,
          justifyContent: 'center',
          display: 'flex'

        }



  <Route path="/Critto" render={() => 


     <div className={classes.divcard}>

                    <Grid  container direction='row' spacing={4}  justify='center'>

                        <Grid item xs={12}>

                            <SimpleImageSlider width={600}  height = {400} images = {imagesSlider} slideDuration = '1'/>

                        </Grid>

                        <Grid item xs={6}>

                          <Card className={classes.cardstats} style = {{color : '#faf7f7', marginTop: 70}}>
                                <CardActionArea>
                                  <CardMedia
                                    className={classes.mediacard}
                                    image={TimeLine}
                                    title="Storia Della Crittografia"
                                  />
                                  <CardContent>
                                    <Typography gutterBottom variant="h5" component="h2" >
                                      Storia Crittografia 
                                    </Typography>
                                    <Typography variant="body2" color="textSecondary" component="p" style = {{color : '#faf7f7'}}>
                                      grrrrr testo quiiiiiii
                                    </Typography>
                                  </CardContent>
                                </CardActionArea>
                                <CardActions>
                                  <Link to="/Critto" style = {{textDecoration : 'none '}}>
                                  <Button  variant="contained" size = 'small' className={classes.buttoncard}>
                                    Learn More
                                  </Button>

                                  </Link>
                                </CardActions>
                          </Card>

                         </Grid>