diff --git a/backend/build.zig b/backend/build.zig
index 70343f752..0b7ba8d55 100644
--- a/backend/build.zig
+++ b/backend/build.zig
@@ -167,7 +167,8 @@ pub fn backendModule(dep: *std.Build.Dependency, dvui_mod: *std.Build.Module, op
         m.addCSourceFile(.{ .file = b.path("src/macos_monitor.m") });
     }
     m.addImport("glass_look", glassLookModule(dep));
-    // A plain dvui app's frame is drawn through the glass's frame target (`plainFrameBegin`). The
+    // A plain dvui app's frame is drawn through the glass's frame target (`plainFrameBegin`), and
+    // its floating windows are made of the glass (`floatingWindowBackground`). The
     // same module as the app's `core` takes (`glassModule`, one per dvui); it imports dvui, never
     // the backend.
     m.addImport("glass", glassModule(dep, dvui_mod));
diff --git a/backend/src/SDLBackend.zig b/backend/src/SDLBackend.zig
index 20cadba6d..3c8bec167 100644
--- a/backend/src/SDLBackend.zig
+++ b/backend/src/SDLBackend.zig
@@ -24,8 +24,9 @@ pub const viewports = @import("viewports.zig");
 pub const os_windows = @import("os_windows.zig");
 /// What this backend keeps count of as it runs (`health`).
 pub const Health = @import("Health.zig");
-/// Fizzy's in-app glass (`src/glass/`): here for `FrameTarget`, a plain dvui app's frame drawn
-/// into a texture (`plainFrameBegin`).
+/// Fizzy's in-app glass (`src/glass/`): a plain dvui app's frame drawn into a texture
+/// (`FrameTarget`, `plainFrameBegin`), and its floating windows made of the window material
+/// (`floatingWindowBackground`).
 pub const glass = @import("glass");
 
 /// What an app gets from its window beyond drawing into it: native dialogs, files the OS hands
@@ -1116,20 +1117,38 @@ pub fn setWindowMaterial(material: MaterialKind, opacity: f32) void {
     window_material = .{ .kind = material, .opacity = opacity };
 }
 
-/// `window_material`, or the best kind below it this backend can show (`materialKinds`).
+/// `window_material`, or the best kind below it this backend can show (`materialKinds`), its
+/// colour less opaque in a light theme (`light_tint`).
 fn effectiveMaterial(self: *SDLBackend) WindowMaterial {
     const offered = self.materialKinds();
+    // In a light theme the window's colour is light over a desktop that is mostly darker, and at
+    // the opacity a dark theme reads well at, little showed through it (the user): a light theme's
+    // colour covers `light_tint` as much. Fizzy's own defaults are the same ratio (`app/settings`:
+    // 0.7 dark, 0.3 light), which fizzy's people set apart; a plain app has the one value.
+    const opacity = if (dvui.themeGet().dark) window_material.opacity else window_material.opacity * light_tint;
     var k = @backingInt(window_material.kind);
     while (k > 0) : (k -= 1) {
         const material: MaterialKind = @fromBackingInt(k);
         const has = switch (material) {
             inline else => |t| @field(offered, @tagName(t)),
         };
-        if (has) return .{ .kind = material, .opacity = window_material.opacity };
+        // Glass keeps a little of the window's colour (`material_min_opacity`); a clear window may
+        // have none.
+        if (has) return .{ .kind = material, .opacity = if (material == .transparent) opacity else @max(opacity, material_min_opacity) };
     }
-    return .{ .kind = .none, .opacity = window_material.opacity };
+    return .{ .kind = .none, .opacity = opacity };
 }
 
+/// The least of the window's colour a material other than a clear window covers what is behind
+/// with: at none, glass is no glass — `glass_look`'s 0, a clear window — and the slider's last
+/// stretch went from a material to none of it (the user). Only `transparent` goes to 0. An app's
+/// own slider stops here (fizzy's does, at the same `glass_look.min_opacity`).
+pub const material_min_opacity: f32 = glass_look.min_opacity;
+
+/// How much of a light theme's window colour covers what is behind, beside a dark theme's at the
+/// same material opacity (`effectiveMaterial`).
+const light_tint: f32 = 0.3 / 0.7;
+
 /// The OS's own title bar on a plain dvui app's windows — the main one and each of the OS's own
 /// frame (`Viewport.native`) — in the theme's colour, made of the window material: set again only
 /// when the theme's colours or the material change. A window opening is dressed as it opens
@@ -1238,6 +1257,51 @@ pub fn floatingWindowTitle(_: *SDLBackend, id: dvui.Id, header: []const u8) bool
     return os_windows.titled(id, header);
 }
 
+/// A floating window of a plain dvui app's, drawn in the main window, made of the window material
+/// (`window_material`, as the backend can show it), as fizzy's own glass is at the same material
+/// (`Editor`'s dialog style): dvui asks where it would fill the window with the theme's colour
+/// (`dvui.Backend.floatingWindowBackground`), with the fill's `rect` and `corners`.
+/// - `none`: dvui's fill, opaque (false: dvui draws it).
+/// - `transparent`: the theme's window colour at the material's opacity over what is behind.
+/// - `frost`, `blur`: what is behind it in the app, frosted (`BlurBackdrop.frostPane`) under that
+///   colour — the frosted pane at the opacity (`glass_look.frosted`), half its blur for `blur`.
+/// - `liquid`: the same, its edge bending what is behind; on macOS with the glass program, Apple's
+///   lens, as the window's own Liquid Glass is beside it (`glass_look.inApp`).
+/// A window fizzy's own frame dresses (`platform.window.app_dresses_windows`) is fizzy's to draw:
+/// its floating windows are its own widget, which never asks.
+pub fn floatingWindowBackground(self: *SDLBackend, id: dvui.Id, rect: dvui.Rect.Physical, corners: dvui.CornerRect.Physical) bool {
+    if (platform.window.app_dresses_windows) return false;
+    const m = self.effectiveMaterial();
+    const fill = dvui.themeGet().color(.window, .fill);
+    switch (m.kind) {
+        .none => return false,
+        .transparent => {
+            rect.fill(corners, .{ .color = .{ .color = fill.opacity(std.math.clamp(m.opacity, 0, 1)) }, .fade = 1 });
+            return true;
+        },
+        .blur, .frost, .liquid => {
+            const opacity = m.opacity;
+            const pane = glass_look.frosted(opacity);
+            const liquid = m.kind == .liquid;
+            // What the glass draws with, as fizzy publishes it each frame (`Editor`): the program
+            // API, and the lens's look while the window is Liquid Glass.
+            glass.programs.publishHost();
+            glass.LiquidField.publishEnabled(liquid);
+            const lens = builtin.target.os.tag == .macos and liquid and glass.LiquidField.ready();
+            glass.LiquidField.publishLook(if (lens) glass_look.inApp(opacity) else null);
+            const s = dvui.windowNaturalScale();
+            glass.BlurBackdrop.frostPane(id, rect, corners.scale(1 / s, dvui.CornerRect), s, .{
+                .radius = if (lens) glass_look.text_blur else if (m.kind == .blur) pane.blur / 2 else pane.blur,
+                .tint = fill,
+                .mix = pane.mix,
+                // Twice the setting, as fizzy's dialogs bend (`core.dialogs.refraction`).
+                .refraction = 2 * (if (lens) 1 else if (liquid) pane.refraction else 0),
+            });
+            return true;
+        },
+    }
+}
+
 /// The kinds of window material this backend can show (fizzy's `core.material`, field for field):
 /// only a kind every surface it puts glass on can show. A clear window everywhere (`transparent`);
 /// on macOS vibrancy (`frost`) and a plain blur, and Liquid Glass from macOS 26; on Windows
diff --git a/docs/DEPENDENCIES.md b/docs/DEPENDENCIES.md
index da132343e..f93b7744e 100644
--- a/docs/DEPENDENCIES.md
+++ b/docs/DEPENDENCIES.md
@@ -154,6 +154,12 @@ as `git+https`: the eight above rebased onto upstream `main` (`41f6703`), then:
 13. **The pointer and its cursor** (`48496b7`, `186a87f`, `1b29a16`): `Window` knows the pointer's
    kind and a lifted finger hovers nothing; `cursorSet` takes a priority, so a resize handle's
    cursor wins, and a floating window's edges ask at normal priority.
+14. **floatingWindow: the backend may draw a floating window's background** (`3d90fdd`):
+   `Backend.floatingWindowBackground(id, rect, corners)`, asked where `FloatingWindowWidget` would
+   fill its background (after its shadow and border, its subwindow current, before its content).
+   True: the backend drew it, and dvui draws no fill. Fizzy's backend draws a plain app's floating
+   windows in the window's material there: a frosted backdrop of what is under them needs the
+   backend's render targets at that point of the replay, which a theme fill cannot express.
 
 Tags: `fizzy-sdk-0.2.13` → `712f7f7` (the stack before this rebase, still what SDK ≤ 0.2.15
 builds); `fizzy-sdk-0.2.16` → `4428108` (SDK 0.2.16 to 0.2.18); `fizzy-sdk-0.2.19` →
@@ -165,8 +171,8 @@ moves, so the second pin of one version takes a suffix, as the SDL fork's tags d
 `fizzy-sdk-0.2.30-3` → `cc60612` (never
 pinned); `fizzy-sdk-0.2.30-4` → `44010a3`; `fizzy-sdk-0.2.30-5` →
 `20e56f1` (never pinned on `main`); `fizzy-sdk-0.2.30-6` → `40e664c`, the last pin on Zig 0.16;
-`fizzy-sdk-0.2.30-7` → `1b29a16` on `zig-0.17`, what `sdk/build.zig.zon` pins now (SDK 0.2.30, the
-first on Zig 0.17).
+`fizzy-sdk-0.2.30-7` → `1b29a16` on `zig-0.17` (SDK 0.2.30, the first on Zig 0.17);
+`fizzy-sdk-0.2.30-8` → `3d90fdd` (item 14), what `sdk/build.zig.zon` pins now.
 
 Fizzy builds dvui in its `custom` backend mode on every target and links its own backends
 (`backend/`, `src/backend/WebBackend.zig` + `web/web.js`), so dvui's `sdl3` and `web`
diff --git a/sdk/build.zig.zon b/sdk/build.zig.zon
index 75b16341c..97717389d 100644
--- a/sdk/build.zig.zon
+++ b/sdk/build.zig.zon
@@ -40,9 +40,10 @@
         // `fizzy-sdk-<version>` tag in the fork before the pin lands. `fizzy-dev` itself stays a
         // working branch and can be rebased freely — the tag, never.
         .dvui = .{
-            // fizzy-sdk-0.2.30-7, on the zig-0.17 branch (docs/DEPENDENCIES.md)
-            .url = "git+https://github.com/foxnne/dvui-dev#1b29a16d0340005c0d5ed2b689a7ffab797b1c37",
-            .hash = "dvui-0.6.0-dev-AQFJmXGtBAE8dNSt4nGJ7ToMZ9HR7rdMVubvTlhzO-mk",
+            // The zig-0.17 branch: fizzy-sdk-0.2.30-7 and the floating window background hook after
+            // it (docs/DEPENDENCIES.md, patch 14)
+            .url = "git+https://github.com/foxnne/dvui-dev#3d90fdda949d50ba7fa82117ccb18a40da5b41cc",
+            .hash = "dvui-0.6.0-dev-AQFJmTG2BAHCy_MTZv6SjCTs3xHXSOPuxEsON67RQ7uS",
             //.path = "../../dvui-dev",
         },
         .zf = .{