Material-UI Responsive Cards

I'm in the process of testing out Material-UI. I've been using Bootstrap for a long time, but am interested in adapting some React projects to Material-UI. Something I've been trying to figure out is how to create responsive cards in Material-UI. I've leaned pretty heavily on Bootstraps responsive containers in the past, so I can't understand why my cards expand with the page but don't shrink as the window is condensed...If we're meant to write custom css for this I'm cool with that, just need to be pointed in the right direction.

Questions:

1. Are responsive cards in Material-UI out of the gate a thing?

2. Or are we meant to write the css to make the cards responsive?

3. If so, where can I learn to do that? (leaned on Bootstrap a lot in the past)

Thanks in advance for your help!

...
useStyles = () => makeStyles(theme => ({
    root: {
      flexGrow: 1,
    },
    paper: {
      padding: theme.spacing.unit,
      textAlign: "center",
      color: theme.palette.text.secondary,
      marginBottom: theme.spacing.unit
    },
  }));

  render() {
    const {baseData} = this.state;
    const {hfcMetrics} = this.state;
    const {stateMember} = this.state;
    const {stateName} = this.state;
    const {states} = this.state;
    const {lineVizData} = this.state;
    const classes = this.useStyles();

    return (this.state.doneLoading === false ? (
      <div className={classes.root}>
        <Grid container>
          <Grid item xs={12}>
            <ReactLoading type={"spinningBubbles"} color={"black"} height={'10%'}
                          width={'10%'} id='spinner'/>
          </Grid>
        </Grid>
      </div>
        ) 
        :
        (stateMember === true ?
      <div className={classes.root}>
        <Grid container spacing={3}>
          <Grid item xs={12}>
            <Card>  
              <CardHeader
                title="Options" 
              />
              <CardContent style={{ width: '100%', height: 300 }}>
                <LineViz 
                  data={lineVizData}
                  state={stateName}
                  source='compareTool'
                  states={states}
                  vizKey={this.state.vizKey}
                  /> 
              </CardContent>
              <CardActions>
                <Button size="small" color="primary">
                  Share
                </Button>
                <Button size="small" color="primary">
                  Learn More
                </Button>
              </CardActions>
            </Card>
          </Grid>
          <Grid item xs={6}>
            <Card ref={this.elRef}>  
              <CardHeader
                title="Comparison Analysis" 
                action={
                  <ButtonGroup variant="text" color="primary" aria-label="text primary button group">
                    <YearDropDown2 
                      year={this.state.year}
                      handleChange={this.toggleYear}
                    /> 
                    <IconButton color='default' component="span"
                      onClick={() => this.resetStateToggle()}><AutorenewRoundedIcon/></IconButton>
                  </ButtonGroup>
                }
              />
              <CardContent style={{padding: 0}}>
                <DataCompareTable
                  data={this.state.compareData} 
                  metric={this.state.metric}
                  stateName={this.state.stateName}
                  compareCount={this.state.compareCount}
                  handleChange={this.toggleStateName}
                  toggleOne={this.state.toggleOne}
                  toggleTwo={this.state.toggleTwo}
                  toggleThree={this.state.toggleThree}
                />
              </CardContent>
            </Card>
          </Grid>
          <Grid item xs={6}>
            <Paper className={classes.paper}>xs=6</Paper>
          </Grid>
        </Grid>
      </div>
      : '' 
      )
    )
  }
}

export default CompareTool