it just follows my qt theme, haven't had any issues with vlc on swayfx

here is my config (qt.nix, using home-manager):

{ pkgs, ...}: {
  qt = {
    enable = true;
    platformTheme.name = "qt5ct"; # compatibility with qt5, while still working with qt6
    style.name = "kvantum";
  };

  xdg.configFile = {
    "Kvantum/Catppuccin-Mocha-Peach".source = "${(pkgs.catppuccin-kvantum.override {accent = "Peach"; variant = "Mocha";})}/share/Kvantum/Catppuccin-Mocha-Peach";
    "Kvantum/kvantum.kvconfig".text = "[General]\ntheme=Catppuccin-Mocha-Peach";
  };

  home.packages = with pkgs; [
    libsForQt5.qt5ct
    kdePackages.qt6ct
  ];
}