Setting the `GTK_THEME` variable doesn't change LO UI appearence

I’m able to change the the UI appearance of my GTK applications by setting the GTK_THEME variable, for example launching thunar with

GTK_THEME=<mytheme> thunar  # Does apply apply <mytheme>

applies <mytheme> to thunar, however this doesn’t work for LO apps. When I launch LO Writer with

GTK_THEME=<mytheme> lowriter  # Doesn't apply <mytheme>

LO Writer launches in a light theme (I’m not sure which one), not even my default theme which is Adwaita:dark.

I’m running Sway, a Wayland compositor, so the only way I change my GTK theme by setting the GTK_THEME variable.

How can I change the UI appearance of LibreOffice with the GTK_THEME variable?