Centering a justify-content space-between once it becomes a single column

I am trying to style a div that has two children, with flexbox and flex-wrap, without media-queries, that at a certain width is space-between, but once it is a single column is centered (as opposed to currently where once it wraps it's like flex-start). Hopefully that makes sense.

I think this is the relevant code, basically when it wraps, i would like space between to become center:

HTML and CSS

.content-container {    display: flex;    justify-content: center;    width: 100%;}.content {    display: flex;    flex-wrap: wrap;    justify-content: space-between;    width: 82%;}.content h1 {    min-width: 20rem;}.content h6 {    min-width: 15.5rem;}

<div class="content-container"><div class="content"><h1>'content1'</h1><h6>'content2'</h6></div></div>