Position element vertically centered in the outer element with known height

index.html

<div class="container">
  <div class="inner">
    <div class="text">
      Lorem ipsum dolor sit amet.
    </div>    
  </div>
</div>

index.scss

* {
  box-sizing: border-box;
}

body{
  padding: 15px;  
}

.container {
  width: 300px;  
  line-height: 300px;
  border: solid 4px blue;
  
  .inner{    
    display: inline-block;
    line-height: 1.25em;
    vertical-align: middle;
    width: 100%;    
    border: solid 4px green;
    
    .text{
      text-align: center;
    }
  }
}