message: Update CSS overrides example
  isSelected is no longer a valid theme entry for MUI Pickers, so update
  the docs to reflect this change. Also extends the example for
  dayDisabled override.
diff: @@ -22,9 +22,12 @@ const materialTheme = createMuiTheme({
  day: {
  color: lightBlue.A700,
  },
  - isSelected: {
  + daySelected: {
  backgroundColor: lightBlue['400'],
  },
  + dayDisabled: {
  + color: lightBlue['100'],
  + },
  current: {
  color: lightBlue['900'],
  },
  @@ -46,6 +49,7 @@ function CssOverrides() {
  label="Light blue picker"
  value={selectedDate}
  onChange={handleDateChange}
  + shouldDisableDate={day => day.getDay() === 0}
  animateYearScrolling={false}
  />
  </ThemeProvider>
  