diff --git a/src/main.rs b/src/main.rs
index 8658643..7ec0602 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,9 +1,11 @@
 mod color_scheme;
 mod config;
 mod icon_index;
+mod ui;
 
 use gtk::prelude::*;
-use gtk::{glib, Application, ApplicationWindow};
+use gtk::{glib, Application, ApplicationWindow, Stack};
+use std::path::{Path, PathBuf};
 
 const APP_ID: &str = "dev.rootiest.IconColorTool";
 
@@ -11,6 +13,24 @@ fn main() -> glib::ExitCode {
     let app = Application::builder().application_id(APP_ID).build();
 
     app.connect_activate(|app| {
+        let breeze_path = match config::load_breeze_path() {
+            Ok(p) => p,
+            Err(e) => {
+                eprintln!("Failed to resolve breeze-icons path: {e:#}");
+                std::process::exit(1);
+            }
+        };
+
+        let initial_arg = std::env::args().nth(1);
+        let initial_icon = initial_arg
+            .as_deref()
+            .map(|a| resolve_icon_arg(a, &breeze_path));
+
+        if let Some(Err(e)) = &initial_icon {
+            eprintln!("Error: {e}");
+            std::process::exit(1);
+        }
+
         let window = ApplicationWindow::builder()
             .application(app)
             .title("Icon Color Tool")
@@ -18,8 +38,68 @@ fn main() -> glib::ExitCode {
             .default_height(650)
             .build();
 
+        let stack = Stack::new();
+        window.set_child(Some(&stack));
+
+        build_picker(&stack, breeze_path);
+
+        if let Some(Ok(path)) = initial_icon {
+            build_editor(&stack, path);
+        }
+
         window.present();
     });
 
     app.run()
 }
+
+fn resolve_icon_arg(arg: &str, breeze_path: &Path) -> anyhow::Result<PathBuf> {
+    let as_given = PathBuf::from(arg);
+    if as_given.is_absolute() {
+        anyhow::ensure!(
+            as_given.exists(),
+            "Icon not found at {}",
+            as_given.display()
+        );
+        return Ok(as_given);
+    }
+    if as_given.exists() {
+        return Ok(as_given.canonicalize()?);
+    }
+    let under_breeze = breeze_path.join(arg);
+    anyhow::ensure!(
+        under_breeze.exists(),
+        "Icon not found at {} or {}",
+        as_given.display(),
+        under_breeze.display()
+    );
+    Ok(under_breeze.canonicalize()?)
+}
+
+fn build_picker(stack: &Stack, breeze_path: PathBuf) {
+    let stack_for_callback = stack.clone();
+    let widget = ui::picker::build_picker_page(breeze_path, move |icon_path| {
+        build_editor(&stack_for_callback, icon_path);
+        stack_for_callback.set_visible_child_name("editor");
+    });
+    stack.add_named(&widget, Some("picker"));
+    stack.set_visible_child_name("picker");
+}
+
+fn build_editor(stack: &Stack, icon_path: PathBuf) {
+    let stack_for_callback = stack.clone();
+    match ui::editor::build_editor_page(&icon_path, move || {
+        stack_for_callback.set_visible_child_name("picker");
+    }) {
+        Ok(widget) => {
+            if let Some(existing) = stack.child_by_name("editor") {
+                stack.remove(&existing);
+            }
+            stack.add_named(&widget, Some("editor"));
+            stack.set_visible_child_name("editor");
+        }
+        Err(e) => {
+            eprintln!("Failed to open {}: {e:#}", icon_path.display());
+        }
+    }
+}