Why are many options missing from the editor?

Switch your editor to use the visual mode instead of the text mode. You’ll find this on the right-hand side of your editor. Also, see the item with a grey box around it in the below image. That’s the “kitchen sink” button. It toggle’s the rest of the toolbar for a deeper list of options.

Adding custom shortcode to page leads to page without styling

Shortcodes need to return their values, but the_content() echoes the post content. So you have two options. First is to capture all output and then return it at the end: ob_start(); // Start capturing output; while( $loop->have_posts() ) { $loop->the_post(); the_content(); }; wp_reset_postdata(); return ob_get_clean(); // Return captured output; That will be the cleanest way … Read more

Forbidden when I’m trying to edit one page

Found the problem, it was caused by ModSecurity module in CPanel. For unknown reasons, it blocks the edit of that WordPress page (only that page). I disabled ModSecurity and works now. I’ll contact my hosting company to see what’s wrong (I cannot make any configuration in my Cpanel for ModSecurity)