bootstrap 5 center
<div class="position-relative">
<div class="position-absolute top-0 start-0 translate-middle"></div>
<div class="position-absolute top-0 start-50 translate-middle"></div>
<div class="position-absolute top-0 start-100 translate-middle"></div>
<div class="position-absolute top-50 start-0 translate-middle"></div>
<div class="position-absolute top-50 start-50 translate-middle"></div>
<div class="position-absolute top-50 start-100 translate-middle"></div>
<div class="position-absolute top-100 start-0 translate-middle"></div>
<div class="position-absolute top-100 start-50 translate-middle"></div>
<div class="position-absolute top-100 start-100 translate-middle"></div>
</div>