First 10% one background color ,another 90% another background color.
<TextField
className={classes.root}
type="text"
placeholder="username"
variant="outlined"
style={{borderRadius:'50',
backgroundColor: "white"
}}
InputProps={{
startAdornment: (
<InputAdornment position="start">
<PersonIcon />
</InputAdornment>
)
}}
/>
I attach demo textfield in below

