html kodları
<div class="iletisimbutonlari btn-group d-flex justify-content-between d-md-none" role="group" aria-label="...">
<a href="tel:xx" class="btn btn-primary ">
<i class="icofont-ui-call"></i> <b> ŞİMDİ ARA</b>
</a>
<a href="https://api.whatsapp.com/send?phone=+xx" target="_blank" class="btn btn-success ">
<i class="icofont-brand-whatsapp"></i> Whatsapp
</a>
</div>

css kodları;
.iletisimbutonlari { position: fixed; width: 100%; z-index: 999; bottom: 0px; left: 0px;}
.iletisimbutonlaria.btn { width: 100%;}
.iletisimbutonlari { position: fixed; display: none; text-align: center; align-items: center; z-index: 99999;}