How can you edit the format of modern style list/library column headers in Sharepoint Online?

Question

Is there a way to format the column headers of a modern list or library in Sharepoint Online?

I would like to make the dividing borders between column headers show up even when you're not hovering over the border, so it's slightly more obvious to less tech savvy folks that you can resize columns by clicking and dragging those border lines. The few solutions that I have found online seem to only apply for classic view lists (e.g. https://natechamberlain.com/2018/07/20/customize-styles-formatting-of-sharepoint-list-column-header-rows/comment-page-1/).

Answer 1

We can create a custom CSS style and inject the CSS on modern pages using SPFx extensions to achieve it.

The following solution with source code for your reference.

SPFx Applications Customiser CSS Injection

Example CSS code:

.ms-DetailsHeader-cell{
    border:1px;
    border-style:groove;
    background-color:lightSkyBlue;
}