Well... something weird is going on for sure.
It remains broken for me after the edit:
still-broken.png
But if I look at it on my phone, even without any changes from my first post in this thread, it works (without the proper indentation):
mobile-working.jpg
However, simulating a mobile device with devTools still leaves it broken (also in the post edited by @Gwen-Dragon):
sim-broken.png
Even though it really seems like it shouldn't matter, here is the versions of Vivaldi I am using:
On my computer with Windows 10 1909 Build 18363
Stable 3.5.2115.81 (64-bit)
Snapshot 3.6.2137.3 (64-bit)
On my phone on Android 10 with OxygenOS 10.3.7
Stable 3.5.2115.80
Snapshot 3.6.2139.3