Theme development

I have an intranet website. You must log in to be able to view content.

I can accomplish this by not giving the permission "View published content" to the Anonymous user role, only to the Authenticated role.

However, this results in a rather nasty looking "Access denied" error page being shown to Anonymous visitors.

What I want to do is to not show "Access denied", but a friendly greating ("Howdy, stranger!" – I'll expand it when I get this working).

After thinking about it, I decided to keep the system 'creation date', but modify it in the view node to adapt the format so that users can see the date with the Italian format (eg. 27 August 2022)
With Views it 's easy, but here I don't know how to do it.
Has anyone already solved this kind of need or know how it could be done?
Thank you very much

Is there responsive Drupal 9 themes that allow easy editing? I just want to have it ready for all platforms (mobile first), and then add my own colors, font sizes etc. I tried Bootstrap 5, made a sub-theme, but it seems much too over my head and nothing I do in the CSS seems to have any effect on the website.

I have a content-type (house) with a date field "field_visiting_date" to indicate when a house can be visited.

Instead of just display the date, I also show how many days there are left until it's visiting day,
so in short, the difference in days between the visiting_day date and today. I currently have in my node display "teaser" twig file:

My theme is a subtheme of Bootstrap5. I only have content in the Main content region and in Sidebar second (nothing in Sidebar first).

On large screens, I want to show them side by side, with the Main content on the Left and the Second sidebar on the right. This happens by default.

On mobile screens, I want to show them stacked, with the Second sidebar on top and the Main content below. Currently, it is the other way round (Main content on top and Second sidebar below). How can I switch them around on mobile?

Im the Wallclock module, I have the following Javascript library defined in wallclock.libraries.yml:

digital:
  css:
    component:
      css/wallclock.css: {}
  js:
    js/digital.js: { weight: -1 }
  dependencies:
     - core/jquery
     - core/jquery.once
     - core/drupal
     - core/drupalSettings

The file js/digital.js contains: