Master page - Hide Open With Explorer button in Ribbon

[EricDeferm]

I've found the following info on the web: Hide the Windows Explorer Button in SharePoint Libraries

When I add the piece of code suggested on the web site to my Seattle.html master page (tested in multiple site collections - non modern sites) I always receive a XML error (see image) stating that my file isn't XML-Compliant. IMHO the reference/syntax to the Ribbon object is not correct in the master page context. Can someone confirm my assumption & provide the correct syntax for referencing the Ribbon from a Master page using CSS? Tx.

[#2]

Are you using online? then it could be that the style has changed did you look it up with the developer tools if it is in this location?

[#3]

Hi @Deleted tx for your prompt reply. Your suggestion of location made me thinking and I realized that I pasted the code not in the right lines within the Master page. After correction,  I no longer obtain any XML warnings. Although I published a major version of the page (and also in preview) the button OWE is still visible in the Ribbon. Any suggestions? Tx.

[#4]

great but did you check if the classes that are used are still the same as the blog post you referred to?

[#5]

Mmmm...might I ask if you are intentionally modifying a SPO master page? If so, my advise is not to do it..use JavaScript injection instead