h2.text-left{
position:relative;
top:50%;
transform: translateY(-50%);
-webkit-transform: translateY(-50%);
-ms-transform: translateY(-50%);
}
Explanation:
The top:50% style essentially pushes the header element down 50% from the top of the parent element. The translateY stylings also act in a similar manner by moving then element down 50% from the top.
Please note that this works well for headers with 1 (maybe 2) lines of text as this simply moves the top of the header element down 50% and then the rest of the content fills in below that, which means that with multiple lines of text it would appear to be slightly below vertically aligned.
A possible fix for multiple lines would be to use a percentage slightly less than 50%.