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>
flex wrap bootstrap
<div class="d-flex flex-wrap">...</div>
columna de dirección flex 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>
align-self: flex-end
align-self-end
justificar el espacio de contenido entre la clase bootstrap
<div class="row d-flex justify-content-between"></div>