You can do this by creating a snippet with the following code. Note this will make centered text the default for all table headings.
.markdown-preview-view th {
text-align:revert;
}
Minimal is designed around my personal usage. The default for HTML tables is centered headers, but I prefer left aligned headers. Unfortunately there isn’t a way that I know of to define the default alignment of table headers without overriding all table header alignment. For me this is preferable over manually defining the alignment on every table.
You can also add a class prefix to the code above and use the cssClasses YAML to use this snippet only on select files.