Left border of grouped buttons missing about lounge-gtk-theme

[5r-kocm]

This occurs when using a new sassc.
When building this theme with version 3.6.1-2 (ubuntu 20.04.1), i got:

No left borders and no rounded corners.

There are many errors in the console, like that:

WARNING on line 169, column 25 of ../build/gtk3-common.scss:
Compound selectors may no longer be extended.
Consider @extend %selected_items, :disabled instead.

I tried to build it with version 3.4.5-1 (ubuntu bionic) and everything became fine.
Correct one:

So, above fixes do not completely solve the problem.

[ptrxyz]

Can confirm, found the same issue. Compiled this for GTK3.24.

[ptrxyz]

Add this to the end of .themes/Lounge-night/gtk.css (and the other versions if it is relevant to you) as a workaround:

.linked > button:not(entry):first-child {
    border-left-color: rgb(37, 37, 37);
}

[pztrn]

This workaround isn't conform to other border's color. Use this instead:

.linked > button:not(entry):first-child {
    border-left-color: rgba(32, 32, 32, 0.3);
}

[johnfactotum]

This is indeed due to a breaking change in Sass. See https://gitlab.gnome.org/GNOME/gtk/-/issues/2237.