Colored squares on a grid layout

I'm still kinda figuring out how to do more complex UIs, so I'll be
making several commits that aren't very interesting to review... such as
this one.

src/main.rs

@@ -17,6 +17,20 @@ fn main() {
     }))
     .add_plugins(EguiPlugin::default())
     .add_plugins(WorldInspectorPlugin::new())
-    .add_systems(Startup, assets::load_assets)
+    .add_systems(
+      Startup,
+      (setup, assets::load_assets, widgets::spawn_cutter_machine_ui),
+    )
     .run();
 }
+
+fn setup(mut commands: Commands) {
+  commands.spawn(Camera2d);
+}
+
+/// Generic utility for despawning entities that have a given component.
+fn despawn<T: Component>(mut commands: Commands, to_despawn: Query<Entity, With<T>>) {
+  for entity in to_despawn {
+    commands.entity(entity).despawn();
+  }
+}

src/widgets.rs

@@ -1 +1,57 @@
 //! Catch-all location for UI bits
+
+use bevy::{
+  color::palettes::{css::*, tailwind::*},
+  prelude::*,
+  ui::Val::*,
+};
+
+pub fn spawn_cutter_machine_ui(mut commands: Commands) {
+  commands.spawn((
+    machine_ui_base(),
+    children![
+      (
+        Node::default(), // TODO: A real node with stuff in it (buttons, maybe?)
+        BackgroundColor(RED.into()),
+        Pickable::default()
+      ),
+      (
+        Node::default(),
+        BackgroundColor(GREEN.into()),
+        Pickable::default()
+      ),
+      (
+        Node::default(),
+        BackgroundColor(BLUE.into()),
+        Pickable::default(),
+      )
+    ],
+  ));
+}
+
+/// The base panel for the machines that manipulate the room cards.
+fn machine_ui_base() -> impl Bundle {
+  (
+    Node {
+      // Position & size
+      position_type: PositionType::Relative,
+      width: Percent(60.0),
+      height: Percent(60.0),
+      top: Percent(20.0),
+      left: Percent(20.0),
+
+      // 5x5 grid, padding & gutters, etc
+      aspect_ratio: Some(1.0),
+      display: Display::Grid,
+      padding: UiRect::all(Val::Px(10.0)),
+      grid_template_columns: RepeatedGridTrack::flex(5, 1.0),
+      grid_template_rows: RepeatedGridTrack::flex(5, 1.0),
+      row_gap: Val::Px(5.0),
+      column_gap: Val::Px(5.0),
+
+      ..default()
+    },
+    BackgroundColor(SLATE_100.into()),
+    BorderRadius::all(Percent(2.0)),
+  )
+}