Note: there is a problem with this build which broke a number of features. We just patched it with r38.2, so please use that instead.
Construct 3 now supports custom editor themes! We're also releasing a theme SDK so third-party developers can start creating custom themes. We're also going to trial an official dark theme shortly - keep an eye on the forums for it coming soon. It'll start as a separate add-on, but if all goes well it'll be made a built-in option.
On top of that we have a number of usability improvements, including further handling of the back button on mobile for more parts of the UI, and reliability improvements to handling the back button too. And as ever, lots of tweaks and bug fixes.
This build also makes quite a significant architectural change: Construct 3 is built entirely around HTML imports, since they are an excellent way to modularise a large web app. Sadly despite their great utility, they've not managed to take off with other browser vendors, so Google are going to start rolling back support for HTML imports in Chrome. But don't worry! We have built a polyfill that completely replaces the feature, and in our testing appears to work identically. To future-proof Construct 3 from changes in Chrome, we've now switched to always using the polyfill, even in Chrome versions that support HTML imports. In theory this won't change anything, but do be on the look out for any extra bugs or quirks that this may have caused.