Extend the border of MUI Select around another element

Question

I have a dropdown menu using MUI Select to sort (AZ, newest-oldest), and I have a button next to it to reverse direction (ZA, oldest-newest). Is it possible to extend the border of the Select (which darkens on hover) around the IconButton ?

Here's a gif of what currently happens: border highlights on hover but goes back to normal when cursor moves to button .

If I just change the both elements are in to variant="outlined" , the outline cuts right through the label of the Select, whereas the Select's outline leave a gap for the label:

If it's not possible to extend the Select's outline around the button, then can I make a new border around the whole element that has the same behavior on hover -- but without doubling the width of the border around the Select? Or can I make a border just around three sides of the little nubbin that's sticking out with the IconButton in it? How might I do that?

Here's the relevant part of my code for that component:

return (
    <FormControl sx={{ minWidth: "152px", mt: 1, }} >
        <Paper sx={{ bgcolor: "#fefcf9", }}>
        <InputLabel id="arrange-by-label">Arrange By</InputLabel>
        <Select
            labelId="arrange-by-label"
            id="arrange-by"
            value={litTextsOrder}
            label="Arrange By"
            onChange={handleLitTextsOrder}
            sx={{ bgcolor: "#fefcf9", minWidth: "132px" }}
        >
            {valuesArr.map((valueArr, index) => {
                return (
                    <MenuItem 
                        key={index} 
                        value={valueArr[0]}
                    >
                        {valueArr[1]} 
                    </MenuItem>
                )
            })}
        </Select>
        <Box component="span">
        <IconButton>
            <CompareArrowsIcon sx={{ transform: "rotate(90deg)"}}/>
        </IconButton>
        </Box>
        </Paper>
    </FormControl>
)

I tried just moving the inside the , but of course that didn't work. Thanks for your help, y'all!

Answer 1

You can do that by target the next element using & + span selector, remove the border right border of the Select and add a border except the left side in the button next to the Select . The hover color is not in a theme, it's hardcoded at this line, so you also have to copy it.

const theme = useTheme();
const hoverColor =
  theme.palette.mode === "light"
    ? "rgba(0, 0, 0, 0.23)"
    : "rgba(255, 255, 255, 0.23)";
const activeColor = theme.palette.primary.main;

<Select
  label="Arrange By"
  sx={{
    bgcolor: "#fefcf9",
    minWidth: "132px",
    "& fieldset": {
      borderTopRightRadius: 0,
      borderBottomRightRadius: 0
    },
    "&&:hover fieldset": {
      borderRight: "none",
      borderLeft: `solid 1px ${hoverColor}`,
      borderTop: `solid 1px ${hoverColor}`,
      borderBottom: `solid 1px ${hoverColor}`
    },
    "&&.Mui-focused fieldset": {
      borderRight: "none",
      borderLeft: `solid 1px ${activeColor}`,
      borderTop: `solid 1px ${activeColor}`,
      borderBottom: `solid 1px ${activeColor}`
    },
    "& + span": {
      display: "flex",
      borderRadius: theme.shape.borderRadius + "px",
      borderTopLeftRadius: 0,
      borderBottomLeftRadius: 0,

      "& button": {
        height: "100%"
      }
    },
    "&:hover + span": {
      borderColor: hoverColor,
      border: `solid 1px ${hoverColor}`,
      borderLeft: "none"
    },
    "&.Mui-focused + span": {
      borderColor: activeColor,
      border: `solid 1px ${activeColor}`,
      borderLeft: "none"
    }
  }}
>