Q:

Cannot center element in the middle of the div

I have this little arrow that i want to put right in the middle of my div to make it look like a carousel/slideshow control, like a next button or a previous button.  I cannot seem to make it work, with or without bootstrap.  
What am i missing?  It is part of a bigger structure, and maybe that's why? 
Here is the Html:

.III{
    height:800px;
    width:100%;
    padding:0;
    margin-top:50px;
    margin-bottom:50px;
    position:relative;
 }
.semn{
    background-color: blue;
    height:90px;
    width:90px;
    border-radius:90px;
    margin:0 auto;
    display: inline-block; 
    text-align: center; 
}
.sagetica{
    display: inline-block; 
    text-align: center;
    margin:0 auto; 
}
 <div class="row">
    <div class="III container-fluid col-md-12">
     <div class="container-fluid">
     <div class="row align-items-center align-self-center ">  
          <div class="stanga col-md-2 text-center ">
             <div class="semn">
              <p class='sagetica'> &lt; </p>
             </div>
          </div>
         </div>
       </div>
    </div>
 </div>

A:

You can use flexbox to solve this issue.  Just apply display flex property to circular div and align items centrally. 
    .semn{
background-color: blue;
height:90px;
width:90px;
border-radius:90px;
margin:0 auto;
display: flex;
align-items: center; 
text-align: center; 
}

