bootstrap input field validation
<form>
<div class="form-row">
<div class="col-md-4 mb-3">
<label for="validationServer01">First name</label>
<input type="text" class="form-control is-valid" id="validationServer01" placeholder="First name" value="Mark" required>
<div class="valid-feedback">
Looks good!
</div>
</div>
<div class="col-md-4 mb-3">
<label for="validationServer02">Last name</label>
<input type="text" class="form-control is-valid" id="validationServer02" placeholder="Last name" value="Otto" required>
<div class="valid-feedback">
Looks good!
</div>
</div>
<div class="col-md-4 mb-3">
<label for="validationServerUsername">Username</label>
<div class="input-group">
<div class="input-group-prepend">
<span class="input-group-text" id="inputGroupPrepend3">@</span>
</div>
<input type="text" class="form-control is-invalid" id="validationServerUsername" placeholder="Username" aria-describedby="inputGroupPrepend3" required>
<div class="invalid-feedback">
Please choose a username.
</div>
</div>
</div>
</div>
<div class="form-row">
<div class="col-md-6 mb-3">
<label for="validationServer03">City</label>
<input type="text" class="form-control is-invalid" id="validationServer03" placeholder="City" required>
<div class="invalid-feedback">
Please provide a valid city.
</div>
</div>
<div class="col-md-3 mb-3">
<label for="validationServer04">State</label>
<input type="text" class="form-control is-invalid" id="validationServer04" placeholder="State" required>
<div class="invalid-feedback">
Please provide a valid state.
</div>
</div>
<div class="col-md-3 mb-3">
<label for="validationServer05">Zip</label>
<input type="text" class="form-control is-invalid" id="validationServer05" placeholder="Zip" required>
<div class="invalid-feedback">
Please provide a valid zip.
</div>
</div>
</div>
<div class="form-group">
<div class="form-check">
<input class="form-check-input is-invalid" type="checkbox" value="" id="invalidCheck3" required>
<label class="form-check-label" for="invalidCheck3">
Agree to terms and conditions
</label>
<div class="invalid-feedback">
You must agree before submitting.
</div>
</div>
</div>
<button class="btn btn-primary" type="submit">Submit form</button>
</form>
