centrar vertical y horizontalmente bootstrap 4
<div class="container h-100">
<div class="row h-100 justify-content-center align-items-center">
<form class="col-12">
<div class="form-group">
<label for="formGroupExampleInput">Example label</label>
<input type="text" class="form-control" id="formGroupExampleInput" placeholder="Example input">
</div>
<div class="form-group">
<label for="formGroupExampleInput2">Another label</label>
<input type="text" class="form-control" id="formGroupExampleInput2" placeholder="Another input">
</div>
</form>
</div>
</div>
Tame Tiger