message: fix: saving custom CSS correctly
diff: @@ -267,7 +267,7 @@ class Header extends React.PureComponent {
  dashboardTitle,
  layout: positions,
  expandedSlices,
  - css,
  + customCss,
  colorNamespace,
  colorScheme,
  dashboardInfo,
  @@ -288,7 +288,7 @@ class Header extends React.PureComponent {
  const data = {
  positions,
  expanded_slices: expandedSlices,
  - css,
  + css: customCss,
  color_namespace: colorNamespace,
  color_scheme: colorScheme,
  label_colors: labelColors,
  