How to center button in Fluent UI Dialog component?

Dialog component in Fluent UI has DialogFooter. I want to place a button inside that footer and I want it to be in the center. How can that be achieved? I'm unable to move it from its default location.

Sample code (taken from [official docs][https://developer.microsoft.com/en-us/fluentui#/controls/web/dialog#IDialogStyles], slightly modified). The most important part should be at the bottom of the code:

import * as React from 'react';
import { Dialog, DialogFooter } from 'office-ui-fabric-react/lib/Dialog';
import { DefaultButton, PrimaryButton } from 'office-ui-fabric-react/lib/Button';
import { ChoiceGroup } from 'office-ui-fabric-react/lib/ChoiceGroup';
import { useBoolean } from '@uifabric/react-hooks';

const modelProps = {
  isBlocking: true,
  topOffsetFixed: true,
};

const options = [
  {
    key: 'A',
    iconProps: { iconName: 'CalendarDay' },
    text: 'Day',
  },
  {
    key: 'B',
    iconProps: { iconName: 'CalendarWeek' },
    text: 'Week',
  },
  {
    key: 'C',
    iconProps: { iconName: 'Calendar' },
    text: 'Month',
  },
];

export const DialogTopOffsetFixedExample: React.FunctionComponent = () => {
  const [hideDialog, { toggle: toggleHideDialog }] = useBoolean(true);
  const [optionSelected, setOptionSelected] = React.useState('A');

  const onChange = (ev: React.FormEvent<HTMLInputElement>, option: any): void => {
    setOptionSelected(option.key);
  };

  return (
    <>
      <DefaultButton secondaryText="Opens the Sample Dialog" onClick={toggleHideDialog} text="Open Dialog" />
      <Dialog hidden={hideDialog} onDismiss={toggleHideDialog} modalProps={modelProps}>
        <ChoiceGroup
          label="Pick one icon"
          options={options}
          // eslint-disable-next-line react/jsx-no-bind
          onChange={onChange}
          required
        />
        {optionSelected === 'A' && (
          <div>
            <h1>Description</h1>
            <div>
              {' '}
              Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et
              dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
              ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu
              fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt
              mollit anim id est laborum.{' '}
            </div>
          </div>
        )}
        {optionSelected === 'B' && (
          <div>
            <h1>Description</h1>
            <div>
              {' '}
              Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et
              dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex
              ea commodo consequat.{' '}
            </div>
          </div>
        )}
        {optionSelected === 'C' && (
          <div>
            <h1>Description</h1>
          </div>
        )}
        <DialogFooter>
          <PrimaryButton onClick={toggleHideDialog} text="Save" />
        </DialogFooter>
      </Dialog>
    </>
  );
};

That looks like this:

How can the button be moved to the center, where I draw the blue "circle"?

You could place a flex container in your DialogFooter and start centering the buttons inside.
Here's an example:

<DialogFooter>
  <div style={{display: "flex", justifyContent: "center"}}>
     <PrimaryButton onClick={toggleHideDialog} text="Save" />
  </div>
</DialogFooter>