I've been ricing my desktop slowly over the years (don't have a lot of time). I've gotten it somewhat down to what I like. I use Archlinux with Open box, polybar, and rofi. I don't use a desktop environment. My question is what are my options for ricing default applications like dolphin or similar apps with default gui's (xsensors) without using a packaged desktop environment. I believe my default theme and icons are Adwaita (GTK-3)
Kvantun for qt themes and lxappearance for gtk themes. In either one you'd have to first download a theme you want and apply it via correct program. You may have to export a shell variable to tell programs to actually use that theme (may not be necessary, I use a lot of flatpaks so for me it is)
The easiest way to get uniform colors in my experience is to full screen a program running the theme, use a dropper tool in Kolourpaint, see the hex color for what I want to change, then search for that hex in the theme file and change it to the one that matches my rice.
Sorry if I'm wrong, but doesn't lxappearance only set the GTK-2 theme? You set the GTK3 theme via dconf or set the GTK3/4 theme using the GTK_THEME env var. There are hardly any apps that use GTK-2 anymore; only one I can think of off the top of my head is PCManFM.