class is-invalid bootstrap code example

Example 1: bootstrap file upload

<form>
  <div class="form-group">
    <label for="exampleFormControlFile1">Example file input</label>
    <input type="file" class="form-control-file" id="exampleFormControlFile1">
  </div>
</form>

Example 2: input with bootstrap

<form>
  <div class="form-group">
    <label for="exampleInputEmail1">Email address</label>
    <input type="email" class="form-control">
    <small id="emailHelp" class="form-text text-muted">Hello, World</small>
  </div>
 </form>