form_set_error highlights only select fields and not other required field types
This was because of CSS overwritten by Zero Point theme, added more classes in my custom CSS file:

    /* .form-item input.error, */
    .form-wrapper .fieldset-wrapper .form-item input.error,
    .form-item textarea.error,
    .form-item select.error {
            border: 2px solid red;
    }