CSS+Flexbox. How to align text to the center of the container?

Question

PHP

Good day.
Tell me how to align the text to the center of the block in each block of the Flex container?
Something tried the options found here and in help, but did not help. Maybe some properties overlap?
https://codepen.io/anon/pen/JJWKBJ

Answer 1

Sergey is absolutely right, but suddenly this is an abstract example) Here on flex

Answer 2

You can also add to those blocks

display: flex;
justify-content: center;
align-items: center