Replace base-ui bundle with a spawning function

src/resources.rs

@@ -1,11 +1,16 @@
 //! Program constants & defaults
 
-use bevy::{color::palettes::css::*, prelude::*};
+use bevy::{
+  color::palettes::{css::*, tailwind::SLATE_100},
+  prelude::*,
+};
 
 #[derive(Debug, Reflect, Resource)]
 #[reflect(Resource)]
 pub struct UiTheme {
-  // TODO: Panes
+  // Colors for the machine UI panes
+  // (and others, but we're not there yet)
+  pub pane_bg: Color,
 
   // Colors for the "Big Red Buttons" (the main actions of the machines)
   // normal
@@ -33,6 +38,8 @@ pub struct UiTheme {
 impl FromWorld for UiTheme {
   fn from_world(world: &mut World) -> Self {
     Self {
+      pane_bg: SLATE_100.into(),
+
       brb_bg: RED.into(),
       brb_border: DARK_RED.into(),
       brb_hover_bg: PINK.into(),