[DatePicker] smaller static date picker on desktop

• I have searched the issues of this repository and believe that this is not a duplicate.

Summary 💡

I'd like the static date picker to be smaller on desktop, perhaps matching the material ui specification:

The specification describes a total width of 256 pixels. material-ui's implementation is 320 pixels wide. This is wide enough to be problematic for my layout.

I'd prefer smaller by default, but a well-supported way to customize sizing would also be fine with me.

Examples 🌈

https://codesandbox.io/s/relaxed-fermat-o3htk?file=/src/Demo.tsx shows both the original formatting and roughly the formatting I'd like. The latter I managed to get with <Box sx={{...}}> (quoting the relevant part below). Unfortunately, it's ridiculously fragile. Eg, I had to adapt it when upgrading from 5.0.0-alpha.26 to 5.0.0-beta.3.

      <Box
        sx={{
          "& > div": {
            minWidth: 256
          },
          "& > div > div, & > div > div > div, & .MuiCalendarPicker-root": {
            width: 256
          },
          "& .MuiTypography-caption": {
            width: DATE_SIZE,
            margin: 0
          },
          "& .PrivatePickersSlideTransition-root": {
            minHeight: DATE_SIZE * 6
          },
          '& .PrivatePickersSlideTransition-root [role="row"]': {
            margin: 0
          },
          "& .MuiPickersDay-dayWithMargin": {
            margin: 0
          },
          "& .MuiPickersDay-root": {
            width: DATE_SIZE,
            height: DATE_SIZE
          }
        }}
      >
        <StaticDatePicker ... />
      </Box>

Motivation 🔦

I'm writing a network video recorder and want a design with a static datepicker in a column. It's static rather than a pop-up because it displays useful context about what dates have video/motion/etc. But space is precious; I have a large main column of video (or tabular data or whatever) to show. So I don't want big touch-friendly targets when I'm on desktop with a mouse or trackpad available.

Start with the StaticDatePicker implementation and the linked CodeSandbox, then compare its desktop dimensions with the Material Design specification. The requested outcome is a 256-pixel-wide static picker by default or a stable, well-supported sizing customization path; verify that the result avoids the fragile selector overrides shown in the issue.