How can I vertically align elements in a div?

Wow, this problem is popular. It's based on a misunderstanding in the vertical-align property. This excellent article explains it:

Understanding vertical-align, or "How (Not) To Vertically Center Content" by Gavin Kistner.

“How to center in CSS” is a great web tool which helps to find the necessary CSS centering attributes for different situations.

In a nutshell _{^{(and to prevent link rot)}}:

• Inline elements (and only inline elements) can be vertically aligned in their context via vertical-align: middle. However, the “context” isn’t the whole parent container height, it’s the height of the text line they’re in. jsfiddle example
• For block elements, vertical alignment is harder and strongly depends on the specific situation:
  • If the inner element can have a fixed height, you can make its position absolute and specify its height, margin-top and top position. jsfiddle example
  • If the centered element consists of a single line and its parent height is fixed you can simply set the container’s line-height to fill its height. This method is quite versatile in my experience. jsfiddle example
  • … there are more such special cases.

Now that Flexbox support is increasing, this CSS applied to the containing element would vertically center the contained item:

.container {
    display: flex;
    align-items: center;
}

Use the prefixed version if you also need to target Internet Explorer 10, and older (< 4.4 (KitKat)) Android browsers:

.container {
    display: -ms-flexbox;
      display: -webkit-flex;
    display: flex;

       -ms-flex-align: center;
    -webkit-align-items: center;
       -webkit-box-align: center;

       align-items: center;
}

I used this very simple code:

HTML:

<div class="ext-box">
    <div class="int-box">
        <h2>Some txt</h2>
        <p>bla bla bla</p>
    </div>
</div>

CSS:

div.ext-box { display: table; width:100%;}
div.int-box { display: table-cell; vertical-align: middle; }

Obviously, whether you use a .class or an #id, the result won't change.

 .outer {
   display: flex;
   align-items: center; 
   justify-content: center;
 }

It worked for me:

.vcontainer {
    min-height: 10em;
    display: table-cell;
    vertical-align: middle;
}