I know this question is a couple years old, but I am surprised to find that no one suggested:
text-align: center;
this is a more universal property than justify-content, and is definitely not unique to grid, but I find that when dealing with text, which is what this question specifically asks about, that it aligns text to the center with-out affecting the space between grid items, or the vertical centering. It centers text horizontally where its stands on its vertical axis. I also find it to remove a layer of complexity that justify-content and align-items adds. justify-content and align-items affects the entire grid item or items, text-align centers the text without affecting the container it is in. Hope this helps.