I came across this interesting example in the documentation for bootstrap 4:
<div class="form-group has-success">
<label class="form-control-label" for="inputSuccess1">Input with success</label>
<input type="text" class="form-control form-control-success" id="inputSuccess1">
<div class="form-control-feedback">Success! You've done it.</div>
<small class="form-text text-muted">Example help text that remains unchanged.</small>
</div>
<div class="form-group has-warning">
<label class="form-control-label" for="inputWarning1">Input with warning</label>
<input type="text" class="form-control form-control-warning" id="inputWarning1">
<div class="form-control-feedback">Shucks, check the formatting of that and try again.</div>
<small class="form-text text-muted">Example help text that remains unchanged.</small>
</div>
<div class="form-group has-danger">
<label class="form-control-label" for="inputDanger1">Input with danger</label>
<input type="text" class="form-control form-control-danger" id="inputDanger1">
<div class="form-control-feedback">Sorry, that username's taken. Try another?</div>
<small class="form-text text-muted">Example help text that remains unchanged.</small>
</div>
However, I noticed that the edits are not displayed in color
The documentation advises to load the CSS file, but it seems that the class "has-danger" is missing
Surprisingly, the class "has-danger" exists in the CSS file of bootstrap 3
https://getbootstrap.com/docs/3.3/dist/css/bootstrap.min.css
In fact, when I use the CSS file of bootstrap 3, the edits are displayed in color
Is there a way to incorporate the "has-danger" class in bootstrap 4 without using Sass?