You may be misunderstanding the concern expressed on that page. A button communicates action when activated; a link communicates navigation (not necessarily "load new page", perhaps just "show new information on current screen"). Using a button for navigation or a link styled like a button for action has potential to thwart these expectations in various ways.

I'll admit, sometimes this makes some sense; you may be building an interaction that doesn't map cleanly onto either "trigger action" or "show information", and you wish to pick and choose the semantics that best fit your needs.

...But then there's the situation you allude to, where you have a button (action) and a link (navigation) and are just trying to make them look the same for consistency. Even if you pull it off visually, the chance that an end-user's client software will misinterpret what you're doing in some way and cause confusion is high.

The distinction between navigation and action seems rather blurry. Two pages often have often different views of the same entity. You’re not really “going somewhere,” particularly if it’s not a full page reload.

But I guess the main point is not to use buttons in your nav bar.

My rule of thumb can be described in two ways:

1) Can you return things to exactly the state they were before simply by hitting the browser's "back" button once? Then use a link. Otherwise use a button.

2) Will this navigation have side effects (eg, change values in the DB)? If so, then use a button. Otherwise, use a link.

Consider this approach:

<form> <button formaction="https://your/destination">Clicky!</button> </form>

Take it fairly seriously. Using the wrong elements and markup messes with screen readers, which makes the web harder to use for people with visual impairments and makes your websites vulnerable to ADA lawsuits. If you need CSS help, there's a lot of free resources for that. Some pitfalls you might run into when styling links and buttons to look alike are font faces, display properties, widths, borders/outlines, and paddings, so check those as your first culprits. You can use aria-roles in a pinch, but really you should use the right tool for the right job.

Total fear mongering. Then you can be sued as well for writing your comment in a too small font.

I've had multiple clients who have been sued for wrong font sizes and incorrect contrast ratios. This is absolutely real and prevalent.

Can't imagine such a lawsuit having any success, unless you have a corrupt judge, who will find or make up any fake reason for a guilty charge.

In real life there are 100 times as many accessibility problems as on any web page – why shouldn't they be sued?