diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 5853dd6..b83c24e 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -25,3 +25,5 @@ jobs:
           zig build -Dshape=studio -Dzon-layout=true --summary all
       - name: Build the replay app
         run: zig build replay --summary all
+      - name: Build the dvui app
+        run: zig build dvui --summary all
diff --git a/dvui/main.zig b/dvui/main.zig
index ba66263..5e3bcb7 100644
--- a/dvui/main.zig
+++ b/dvui/main.zig
@@ -2,13 +2,12 @@
 //! through `dvui.osWindow` — nothing of fizzy the editor, and nothing but dvui in the app's code.
 //!
 //! On fizzy's backend each `dvui.osWindow` is a floating window in the one frame, shown in an OS
-//! window of its own that looks just as the floating window does in the main window: dvui's header
-//! and close button, no OS title bar. The OS moves it by its header; it resizes itself from its
-//! edges, as a floating window does, and its window follows. The backend does all of it
-//! (`backend/src/os_windows.zig` in fizzy). On dvui's own SDL3 backend (`-Ddvui-backend=sdl3`)
-//! `dvui.osWindow` opens a `dvui.Window` of its own instead, as dvui does anywhere.
-//!
-//! dvui's demo is a floating window, and stays one: in the main window, as in dvui's own example.
+//! window of its own: the OS's title bar and buttons in the theme's colour, as on the main window,
+//! and the floating window's content below. The OS moves, resizes, zooms and closes it; on macOS it
+//! is an ordinary window, with a full screen of its own. The backend does all of it
+//! (`backend/src/os_windows.zig` in fizzy). Every other floating window, dvui's demo among them,
+//! stays in the main window, as in dvui's own example. On dvui's own SDL3 backend
+//! (`-Ddvui-backend=sdl3`) `dvui.osWindow` opens a `dvui.Window` of its own instead.
 const std = @import("std");
 const dvui = @import("dvui");
 
@@ -23,8 +22,10 @@ pub const main = dvui.App.main;
 pub const panic = dvui.App.panic;
 pub const std_options: std.Options = .{ .logFn = dvui.App.logFn };
 
-/// An OS window of the app's own.
+/// A window of the app's own: an in-app floating window, which can be dragged out into an OS window
+/// of its own on fizzy's backend, or a `dvui.osWindow`.
 const Window = struct {
+    os: bool,
     open: bool = true,
     title_buf: [32:0]u8 = @splat(0),
     title_len: usize = 0,
@@ -34,52 +35,97 @@ const Window = struct {
         return self.title_buf[0..self.title_len :0];
     }
 };
-var windows: [4]?Window = @splat(null);
+var windows: [6]?Window = @splat(null);
 var made: u32 = 0;
 var started = false;
 
 fn frame() !dvui.App.Result {
-    // dvui's demo and two OS windows to begin with.
+    // dvui's demo, in the main window, to begin with. An OS window opens only when one is asked
+    // for ("New window"), or when a floating window is dragged out of the app's windows.
     if (!started) {
         started = true;
         dvui.Examples.show_demo_window = true;
-        newWindow();
-        newWindow();
     }
     mainWindow();
+    // dvui's demo first: a window opens over those opened before it, and the demo, centred and much
+    // the larger, hid the app's own windows opened under it.
+    dvui.Examples.demo(.lite);
     for (&windows, 0..) |*slot, i| if (slot.*) |*w| {
         if (!w.open) {
             slot.* = null;
             continue;
         }
-        osWindow(w, i);
+        if (w.os) osWindow(w, i) else floatWindow(w, i);
     };
-    dvui.Examples.demo(.lite);
     return .ok;
 }
 
 fn mainWindow() void {
+    // No fill of its own: the window's colour is the backend's, under what the window is made of
+    // (`materialPicker`), the theme's window colour at the transparency asked.
     var box = dvui.box(@src(), .{}, .{ .expand = .both, .padding = .all(16) });
     defer box.deinit();
     dvui.labelNoFmt(@src(), "dvui's own widgets on fizzy's backend.", .{}, .{ .font = .theme(.title) });
-    dvui.labelNoFmt(@src(), "Each window opened here is a dvui.osWindow.", .{}, .{});
-    if (dvui.button(@src(), "New window", .{}, .{ .margin = .{ .y = 12 } })) newWindow();
+    dvui.labelNoFmt(@src(), "A window opens in the app, and drags out into one of its own; an OS window opens as one.", .{}, .{});
+    {
+        var row = dvui.box(@src(), .{ .dir = .horizontal }, .{ .margin = .{ .y = 12 } });
+        defer row.deinit();
+        if (dvui.button(@src(), "New window", .{}, .{})) newWindow(false);
+        if (dvui.button(@src(), "New OS window", .{}, .{})) newWindow(true);
+    }
     if (!dvui.Examples.show_demo_window) {
         if (dvui.button(@src(), "Show the dvui demo", .{}, .{})) dvui.Examples.show_demo_window = true;
     }
+    if (comptime @hasDecl(dvui.backend, "window_material")) materialPicker();
 }
 
-fn newWindow() void {
+/// What the app's windows are made of, on fizzy's backend: opaque, clear, blurred, frosted or
+/// Liquid Glass, each falling back to what the OS can show, and how transparent. The colour is the
+/// theme's window colour (dvui's theme picker).
+fn materialPicker() void {
+    const B = dvui.backend;
+    var row = dvui.box(@src(), .{ .dir = .horizontal }, .{ .margin = .{ .y = 12 } });
+    defer row.deinit();
+    const names = [_][]const u8{ "Opaque", "Clear", "Blur", "Frost", "Liquid Glass" };
+    var choice: usize = @backingInt(B.window_material.kind);
+    if (dvui.dropdown(@src(), &names, .{ .choice = &choice }, .{}, .{ .min_size_content = .{ .w = 140 }, .gravity_y = 0.5 })) {
+        B.window_material.kind = @fromBackingInt(@as(u8, @intCast(choice)));
+        // Opaque, the window's colour covers it whole: half, to begin with.
+        if (B.window_material.kind != .none and B.window_material.opacity >= 1) B.window_material.opacity = 0.5;
+    }
+    dvui.labelNoFmt(@src(), "Transparency", .{}, .{ .gravity_y = 0.5, .margin = .{ .x = 12 } });
+    var transparency = if (B.window_material.kind == .none) 0 else 1 - B.window_material.opacity;
+    if (dvui.slider(@src(), .{ .fraction = &transparency }, .{ .min_size_content = .{ .w = 160, .h = 20 }, .gravity_y = 0.5 })) {
+        // Transparent at all, it is made of something: clear, where it was opaque.
+        if (B.window_material.kind == .none and transparency > 0) B.window_material.kind = .transparent;
+        B.window_material.opacity = 1 - transparency;
+    }
+}
+
+
+fn newWindow(os: bool) void {
     const slot = for (&windows) |*slot| {
         if (slot.* == null) break slot;
     } else return;
     made += 1;
-    slot.* = .{};
+    slot.* = .{ .os = os };
     const w = &slot.*.?;
-    const t: []const u8 = std.fmt.bufPrint(&w.title_buf, "Window {d}", .{made}) catch "";
+    const t: []const u8 = std.fmt.bufPrint(&w.title_buf, "{s} {d}", .{ if (os) "OS window" else "Window", made }) catch "";
     w.title_len = t.len;
 }
 
+/// An in-app floating window: on fizzy's backend, dragged by its header past the app's windows it
+/// tears off into an OS window of its own (its close button, `open_flag`, is what lets it).
+fn floatWindow(w: *Window, i: usize) void {
+    var float = dvui.floatingWindow(@src(), .{ .open_flag = &w.open, .window_avoid = .nudge }, .{
+        .id_extra = i,
+        .min_size_content = .{ .w = 220, .h = 120 },
+    });
+    defer float.deinit();
+    float.dragAreaSet(dvui.windowHeader(w.title(), "", &w.open));
+    windowContent(w);
+}
+
 fn osWindow(w: *Window, i: usize) void {
     var os = dvui.osWindow(@src(), .{
         .title = w.title(),
@@ -87,6 +133,10 @@ fn osWindow(w: *Window, i: usize) void {
         .min_size = .{ .w = 220, .h = 120 },
     }, .{ .id_extra = i, .open_flag = &w.open });
     defer os.deinit();
+    windowContent(w);
+}
+
+fn windowContent(w: *Window) void {
     var box = dvui.box(@src(), .{}, .{ .expand = .both, .padding = .all(12) });
     defer box.deinit();
     dvui.label(@src(), "Clicked {d} times", .{w.count}, .{});