I have success with outline custom styling when variant="outlined" and I use notchedOutline in InputProps.
Otherwise - variant=[anything else] where only a bottom border exists - it doesn't work, even with underline as the key/class in InputProps.
I've even tried root.
export default ({ boxType, classes, value, onChange, style }) => (
<TextField
variant={boxType || "standard"}
value={value}
onChange={onChange}
InputProps={{
classes: {
notchedOutline: classes.notchedOutline,
underline: classes.underline,
root: classes.TextInputField
},
style
}}
/>
)
