You can easily solve this problem by making the margin of div container to auto that will make it align center to the page
Make your div:

<div class="container text-center">

To:

<div class="container my-auto text-center">

It turned out it happened on specific browser on phone, the one that shows website incorrectly is UC Browser. You can check it out on your own at this website: https://jawegiel-web.herokuapp.com/home

horizontal center

justify-content: center;

vertical center

align-items: center; 

This is my code:

<div class="container text-center">
   <br><br><br><br>

   <a href="" class="btn btn-primary" ng-mousemove="count = count + 1"> Counter </a>
   <br><br><br>
   <h2>{{ count }}</h2>
   <br>
</div>

I us3e bootstrap so this text-center should do the job and give an effect to this >h2> element. But it works only partial that is on high resolution it works but on my mobile phone does not. How to solve this?

This is my screenshot of website on my phone: