Check out example codes for "css vertical center". It will help you in understanding the concepts better.

Code Example 1

.parent-class {
  display: flex;
  align-items: center;
  justify-content: space-around;
}

Code Example 2

/* No Flexbox */
.parent {
  position: relative;
}
.child {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);
}

/* With Flexbox */

.parent {
  display: flex;
  flex-direction: column;
  justify-content: center;
}

Code Example 3

.center {
  display: flex;
  justify-content: center;
  
  align-items: center;
  height: 200px;
  border: 3px solid 
  green; 
}

Code Example 4

<style>
.container { 
  height: 200px;
  position: 
  relative;
  border: 3px solid green; 
}

.center {
  margin: 0;
  
  position: absolute;
  top: 50%;
  left: 50%;
  -ms-transform: 
  translate(-50%, -50%);
  transform: translate(-50%, -50%);
}
</style>

<div 
  class="container">
  <div class="center">
    
  <p>I am vertically and horizontally centered.</p>
  </div>
</div>

Code Example 5

<style>
.container {
  height: 200px;
  position: relative;
  border: 3px solid green;
}

.center {
  margin: 0;
  position: absolute;
  top: 50%;
  left: 50%;
  -ms-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
}
</style>

<div class="container">
  <div class="center">
    <p>I am vertically and horizontally centered.</p>
  </div>
</div>

Code Example 6

/* HTML: */
<div class="text">
lorem ipsum
</div>


/* CSS: */
.text {
vertical-align: middle;
/*can take any value of:
baseline | sub | super | text-top | text-bottom | middle | top | bottom | <percentage> | <length> */
}

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