customize material ui textfield underline using styled component
import TextField from "@material-ui/core/TextField";
import styled from "styled-components";
const StyledTextField = styled(TextField)`
  /* default */
  .MuiInput-underline:before {
    border-bottom: 2px solid green;
  }
  /* hover (double-ampersand needed for specificity reasons. */
  && .MuiInput-underline:hover:before {
    border-bottom: 2px solid lightblue;
  }
  /* focused */
  .MuiInput-underline:after {
    border-bottom: 2px solid red;
  }
`;
export default StyledTextField;
