This has long been the bane of CSS, but has now been fixed using "flex" boxes. On your site, you should add this CSS to the element with the classes et_pb_row.et_pb_row_0
:
display: flex;
align-items: center;
justify-content: center;
Here's some further reading: https://www.adam-bray.com/2017/02/17/simple-css-alignments-with-flexbox/
Hope that helps