checkFullScreen () {
    let state = this.state
    if (this.mobilecheck() === true) {
      styles({dialogPaper: 'block'})
      this.setState(state)
    }
  }

const styles = theme => ({
  dialogPaper: {
    height: '90%'
  },
})

Function

checkFullScreen () {
    let state = this.state
    if (this.mobilecheck() === true) {
      styles({dialogPaper: 'block'})
      this.setState(state)
    }
  }

Return (where the css is being set)

return (

      <Dialog
        open={this.props.open}
        className={classes.dialog}
        classes={{paper: classes.dialogPaper}}
      >