Automatic dark mode for embedded comments as well?

Automatic Dark Mode color scheme switching is a fantastic addition, thanks for integrating it!

With (automatic) color scheme switching available, I’m wondering if there might also be some way to switch back and forth between light and dark Discourse modes when embedded as comments in a blog. Specifically, my Ghost blog has a toggle that users can click on to manually switch back and forth between light and dark modes. I know that my blog’s CSS can’t effect the CSS within Discourse’s iframe, but with this new addition might there be another way that the toggle could also switch the Discourse color scheme? You can see an example post with comments at the bottom of this post.


This is potentially doable but a little tricky. At the moment, we haven’t added dark mode auto switching to the embedded comments endpoint. We can add that, and it would work if your Ghost site was auto-switching to dark mode when the browser switches to dark mode. But from what I can tell, your Ghost site uses a dark mode button, which won’t work with the Discourse implementation.

What you can do in your specific case, is toggle a class in the Discourse embedded comments iframe when clicking the button, and then use that class to toggle colors in your embedded stylesheet.


Sounds good. While I am currently putting together several dark mode utilizing (Ghost) themes for colleagues of mine, all of which will share a single Discourse instance, that’s still a bit further down the road.

I unfortunately don’t quite understand what you’re suggesting here. Currently, any elements that I want to utilize dark mode styling within my blog have their CSS doubled up by preceding such items with body.dark. As in

p {
    color: #000;
body.dark p {
    color: #FFF;

Might you be suggesting that I use that body.dark code to change things in the Discourse iframe? Because I tried inserting the following into Discourse’s Embedded CSS field, which unfortunately had no effect:

.FF2F-discourse p {
    color: #000;
body.dark .FF2F-discourse p {
    color: #FFF;

That being so, are you instead suggesting that I have some separate JS written so that the toggle will affect a separate change via specific targeting of a class in the iframe? Because like I stated in my previous comment, I didn’t think that external coding could affect CSS within an iframe, hence my confusion. But I’m very much solely an HTML/CSS amateur, so there’s no doubt that you know better than me and/or that I’m misunderstanding something else.

Thanks again for any hints.


Yes, that’s what I am suggesting. Your blog’s stylesheets cannot apply to the iframe, but you can use JS to toggle the dark class in the iframe’s html or body element, and then update your Discourse embedded stylesheet accordingly.


I’ve found two pages explaining how toggling between light and dark modes for Discourse’s embed might be done, but the guy who writes my JS is wondering if the method you’re suggesting entails using postMessage (which the pages I found state) or something else.

Here’s a page explaining how to implement cross-window messaging with postMessage

While this one is actually a tutorial on how to change the CSS within an iframe via postMessage, specifically for switching between light and dark modes:

Might I be on the right track with all this?


My apologies, I forgot to respond here, yes, I think postMessage can work for your use case.