alinear elementos centro bootstrap
<div class="d-flex align-items-start">...</div>
<div class="d-flex align-items-end">...</div>
<div class="d-flex align-items-center">...</div>
<div class="d-flex align-items-baseline">...</div>
<div class="d-flex align-items-stretch">...</div>
ustify-contenido: flex-end
<div class="d-flex justify-content-end">...</div>
justify-content-between bootstrap 4
<div class="d-flex justify-content-start">...</div>
<div class="d-flex justify-content-end">...</div>
<div class="d-flex justify-content-center">...</div>
<div class="d-flex justify-content-between">...</div>
<div class="d-flex justify-content-around">...</div>
bootstrap justify-content-center para md
<div class="row justify-content-md-center"></div>
justificar texto bootstrap
<p class="text-justify"> your text for example : Hellow! World.. </p>
justificar el espacio de contenido entre la clase bootstrap
<div class="row d-flex justify-content-between"></div>