HTML Export shows page layout sections on new lines

Summary

Side-by-side sections on a Confluence page will show as on top of each other when exported to HTML.

Steps to Reproduce

1. Create a page that has a page layout section with multiple columns.
   
2. Save the page
   
3. Export the space to HTML
4. View the page

Expected Results

The sections will show side-by-side, as they do on the page.

Actual Results

The sections are stacked on top of each other.

Workaround

Add the following at the end of the styles/site.css file in the export:

.columnLayout {
    display: flex;
}

.cell {
    flex: auto;
}