Change Default Category Based On Conditions

We have the Pavilion Event plugin which creates a /Calendar page.

I’m looking to tweak the calendar page using CSS/HTML/Theme Components to make it as user-friendly as possible.

Because we only have a few categories that we allow Events to be created in, i have successfully filtered the category drop-down in the composer to only include the relevant categories.

The part i’m struggling on is setting the default category in the composer using CSS/HTML (so i can use conditions to trigger it on the correct pages - like the calendar page).

The aim is everywhere else on the Discourse the default category is ‘General’, but if the user is creating a topic from the Calendar page ( the page already has the ‘New Topic’ functionality) - the composer’s category defaults to ‘Event Planning’ instead, and triggers the template attached to the ‘Event Planning’ category.

Can anyone point me in the right direction?


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For reference - the code i’ve gotten so far:


<!-- Used to flag Calendar page by adding calendar-page class to body -->

    // Check if the URL ends with "/calendar"
    if (window.location.href.endsWith("/calendar")) {
      // Add a class to the body to trigger the CSS rule

<!-- Changes 'Add Topic' to 'Add Event' in calendar screen -->

    // Check if the body has the class "hide-on-calendar"
    if (document.body.classList.contains('calendar-page')) {
      // Update the text of the button
      const button = document.querySelector('.main-content.calendar .d-button-label');
      if (button) {
        button.textContent = 'Add Event';


//Hide none Event Categories 
     body.calendar-page[title]:not([title="Private Events"]):not([title="Public Events"]):not([title="Induction Sessions"]):not([title="Space Bookings"]) {
      display: none;

If anyone has got any suggestions on how to pick up a value set against the category settings by a plugin (in this case the Event’s plugin’s “Allow events to be added to topics in this category.” setting) so i don’t need to hard code the categories, that would be awesome too … but i know i’m pushing my luck.