How to force a border when only one app onscreen

[Whyglobaleyes]

Hello,
I just realised - and it's slightly weird that - it gives me a good feeling to be talking to folks who appreciate regolith. Morning all.

I've got a niggle that I've never addressed and is a nice-to-have rather than essential config. As per the title: I'd like to force a border round app windows when there's only one app on the screen. I suspect that there's an Xresources value I need to set but I can't figure out how to do it. Could anyone help please?

• Set-up: Debian GNU/Linux 11 (bullseye) :: REGOLITH_VERSION=2.1 :: Multi-monitor setup (but it's the same with single monitor)
• my ~/.config/regolith2/i3/config.d/conf file has:

for_window [class=.*] border pixel 002
for_window [class="Yad"] floating enable

• my ~/.config/regolith2/Xresources file has:

i3-wm.window.border.size: 5
i3-wm.gaps.inner.size: 0
i3-wm.gaps.outer.size: 2
i3-wm.client.focused.color.child_border: #ffff00
i3-wm.gaps.smart: off
i3-wm.bar.background.color: #000000
i3-wm.bar.workspace.active.background.color: #000000
i3-wm.bar.workspace.active.border.color: #000000
i3-wm.bar.workspace.active.text.color
i3-wm.bar.workspace.focused.background.color: #d4bf24
i3-wm.bar.workspace.focused.border.color
i3-wm.bar.workspace.focused.text.color: #000000
regolith.look.path: /usr/share/regolith-look/ayu-dark