How to use the netlify-cms-ui-default.colors.background function in netlify-cms-ui-default

);

const styles = {
  toast: css`
    ${shadows.drop};
    background-color: ${colors.background};
    color: ${colors.textLight};
    border-radius: ${lengths.borderRadius};
    margin: 10px;
    padding: 20px;
    overflow: hidden;
  `,
  info: css`
    background-color: ${colors.infoBackground};
    color: ${colors.infoText};
  `,
  success: css`
    background-color: ${colors.successBackground};
    color: ${colors.successText};
  `,
  warning: css`
    background-color: ${colors.warnBackground};

`;

const NoPreviewContainer = styled.div`
  ${styles.splitPane};
`;

const EditorContainer = styled.div`
  width: 100%;
  min-width: 800px;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  overflow: hidden;
  padding-top: 66px;
  background-color: ${colors.background};
`;

const Editor = styled.div`
  height: 100%;
  margin: 0 auto;
  position: relative;
`;

const PreviewPaneContainer = styled.div`
  height: 100%;
  overflow-y: auto;
  pointer-events: ${props => (props.blockEntry ? 'none' : 'auto')};
`;

const ControlPaneContainer = styled(PreviewPaneContainer)`
  padding: 0 16px;

margin-bottom: ${bottomMargin};
  white-space: pre-wrap;

  & > code {
    display: block;
    width: 100%;
    overflow-y: auto;
    background-color: #000;
    color: #ccc;
    border-radius: ${lengths.borderRadius};
    padding: 10px;
  }
`;

const StyledCode = styled.code`
  background-color: ${colors.background};
  border-radius: ${lengths.borderRadius};
  padding: 0 2px;
  font-size: 85%;
`;

const StyledUl = styled.ul`
  margin-bottom: ${bottomMargin};
  padding-left: 30px;
`;

const StyledOl = StyledUl.withComponent('ol');

const StyledLi = styled.li`
  & > p:first-child {
    margin-top: 8px;
  }

li > p {
    margin: 0;
  }

  ul,
  ol {
    padding-left: 30px;
  }

  pre {
    white-space: pre-wrap;
  }

  code {
    background-color: ${colors.background};
    border-radius: ${lengths.borderRadius};
    padding: 0 2px;
    font-size: 85%;
  }

  pre > code {
    display: block;
    width: 100%;
    overflow-y: auto;
    background-color: #000;
    color: #ccc;
    border-radius: ${lengths.borderRadius};
    padding: 10px;
  }

  blockquote {