How to add custom button in WYSIWYG editor?

Okay, I found out from there that this is what I need https://getpublii.com/dev/post-editor-api/#customformats but it simply doesn’t work for me. I might have done something wrong but idk what. Here’s what I’ve done.

#1 In Documents\Publii\themes\technews i opened config.json file and added this code https://prnt.sc/8hi2dJEPlr9h

#2 After I saved config.json file, I opened my theme’s root directory (Documents\Publii\themes\technews) and created the following two files: tinymce.override.json and customElements.json

#3 The content of tinymce.override.json:

{
   "toolbar2": "customElements nonbreaking styleselect formatselect searchreplace hr readmore removeformat undo redo restoredraft sourcecode ",
   "plugins": "nonbreaking advlist autolink autosave link image lists hr pagebreak searchreplace media table paste autoresize emoticons textpattern toc"
}

#4 The content of customElements.json:

"customElements": [
    {
        "label": "Cvars",
        "cssClasses": "msg msg--cvars",
        "selector": "p"
        "postEditor": true,
        "themeSettings": true		
    },
    {
        "label": "Commands",
        "cssClasses": "msg msg--cmds",
        "selector": "p"
        "postEditor": true,
        "themeSettings": false			
    },
    {
        "label": "Warning",
        "cssClasses": "msg msg--warning",
        "selector": "p"
        "postEditor": true,
        "themeSettings": false			
    }
] 

#5 I also added CSS classes for those formats in Documents\Publii\themes\technews\assets\css\editor.css file.

And I still don’t have new custom formats added in my editor when writing the post. Where did I made a mistake?