diff --git a/docs/swarm/ui.md b/docs/swarm/ui.md
index 11ce8fd60..b80b3232a 100644
--- a/docs/swarm/ui.md
+++ b/docs/swarm/ui.md
@@ -129,10 +129,6 @@ you flip it. It also hides the **components** tab, a page for developers, which
 still answers at `/components`. The browser keeps the choice for the swarm UI, apart from the
 per-agent pages'.
 
-The menu also has a **solid backgrounds** toggle. It turns the frosted, see-through
-surfaces opaque: the header bar, the badges and the terminal panes. It stays off
-until you turn it on, and the browser keeps the choice.
-
 The menu also has an **expand tool output** toggle. It opens tool-output rows
 expanded; rows already on screen keep their state, and rows that arrive after
 you flip it follow it.
diff --git a/frontend/packages/shared/package.json b/frontend/packages/shared/package.json
index 4d004381d..0d5718e34 100644
--- a/frontend/packages/shared/package.json
+++ b/frontend/packages/shared/package.json
@@ -55,7 +55,6 @@
     "./hide-debug-setting.js": "./src/settings/HideDebugSetting.tsx",
     "./expand-details-setting.js": "./src/settings/ExpandDetailsSetting.tsx",
     "./settings-menu.css": "./src/settings/SettingsMenu.css",
-    "./solid-backgrounds.js": "./src/settings/solid-backgrounds.tsx",
     "./user-menu.js": "./src/user-menu/UserMenu.tsx",
     "./user-menu.css": "./src/user-menu/UserMenu.css",
     "./links-menu.js": "./src/links-menu/LinksMenu.tsx",
diff --git a/frontend/packages/shared/src/settings/solid-backgrounds.css b/frontend/packages/shared/src/settings/solid-backgrounds.css
deleted file mode 100644
index eaf63c476..000000000
--- a/frontend/packages/shared/src/settings/solid-backgrounds.css
+++ /dev/null
@@ -1,20 +0,0 @@
-/* The frosted surfaces, made opaque while `data-solid="true"` is on `<html>`
-   (`solid-backgrounds.tsx`). Each rule names the same surface as the rule that
-   makes it see-through, with `html:root` in front so it outranks that rule's
-   theme variants whatever order the stylesheets load in. The dialog scrim is
-   left alone: it dims the page on purpose. */
-html:root[data-solid="true"] .shell-header {
-  background: var(--bg-elev);
-  -webkit-backdrop-filter: none;
-  backdrop-filter: none;
-}
-html:root[data-solid="true"] .ui-badge:not(.ui-badge-quiet) {
-  background: var(--purple-dim);
-  -webkit-backdrop-filter: none;
-  backdrop-filter: none;
-}
-html:root[data-solid="true"] .terminal-wrap {
-  background: var(--crust);
-  -webkit-backdrop-filter: none;
-  backdrop-filter: none;
-}
diff --git a/frontend/packages/shared/src/settings/solid-backgrounds.tsx b/frontend/packages/shared/src/settings/solid-backgrounds.tsx
deleted file mode 100644
index c7ce9ea07..000000000
--- a/frontend/packages/shared/src/settings/solid-backgrounds.tsx
+++ /dev/null
@@ -1,39 +0,0 @@
-// "Solid backgrounds" — a gear-menu toggle that turns the frosted, see-through
-// surfaces opaque (mara: "add setting to disable transparency", e.g. the top
-// bar and badge backgrounds). Off by default, so the look is unchanged until
-// someone turns it on.
-//
-// The setting sets `data-solid="true"` on `<html>`, and `./solid-backgrounds.css`
-// answers it. The caller owns the storage key, as with the theme and motion
-// overrides, and mounts `useApplySolidBackgrounds` once so the choice applies
-// before the menu is ever opened; `SolidBackgroundsSetting` is the menu's row.
-import { useEffect } from "preact/hooks";
-import { useLocalSetting } from "./settings-storage.js";
-import "./solid-backgrounds.css";
-
-export function useApplySolidBackgrounds(key: string): void {
-  const [solid] = useLocalSetting<boolean>(key, false);
-  useEffect(() => {
-    const root = document.documentElement;
-    if (solid) root.dataset.solid = "true";
-    else delete root.dataset.solid;
-  }, [solid]);
-}
-
-export function SolidBackgroundsSetting({
-  storageKey,
-}: {
-  storageKey: string;
-}) {
-  const [solid, setSolid] = useLocalSetting<boolean>(storageKey, false);
-  return (
-    <label class="settings-menu-row">
-      <span>solid backgrounds</span>
-      <input
-        type="checkbox"
-        checked={solid}
-        onChange={(e) => setSolid((e.target as HTMLInputElement).checked)}
-      />
-    </label>
-  );
-}
diff --git a/frontend/packages/swarm-ui/src/shell/Shell.tsx b/frontend/packages/swarm-ui/src/shell/Shell.tsx
index b3dc60380..4d59b5d87 100644
--- a/frontend/packages/swarm-ui/src/shell/Shell.tsx
+++ b/frontend/packages/swarm-ui/src/shell/Shell.tsx
@@ -37,10 +37,6 @@ import { HideDebugSetting } from "@hive/shared/hide-debug-setting.js";
 import { ExpandDetailsSetting } from "@hive/shared/expand-details-setting.js";
 import { useApplyThemeOverride } from "@hive/shared/theme-apply.js";
 import { useApplyMotionOverride } from "@hive/shared/motion-apply.js";
-import {
-  SolidBackgroundsSetting,
-  useApplySolidBackgrounds,
-} from "@hive/shared/solid-backgrounds.js";
 import { isFullBleedRoute, visibleNavItems } from "./routes.js";
 import { useDynamicTabs } from "./useDynamicTabs.js";
 import { useSwarmName } from "./useSwarmName.js";
@@ -53,7 +49,6 @@ import "./Shell.css";
 // not `'system'` — see `@hive/shared/theme-apply.js`'s file comment.
 const THEME_KEY = "swarm-ui:theme-override";
 const MOTION_KEY = "swarm-ui:motion-override";
-const SOLID_KEY = "swarm-ui:solid-backgrounds";
 
 const NAV_ITEMS: { href: string; label: string; accent: string }[] = [
   { href: "/agents", label: "agents", accent: "var(--green)" },
@@ -225,7 +220,6 @@ export function Shell({ children }: { children: ComponentChildren }) {
   // needing a reference to the other.
   useApplyThemeOverride(THEME_KEY);
   useApplyMotionOverride(MOTION_KEY);
-  useApplySolidBackgrounds(SOLID_KEY);
 
   // Measures nav item `index`'s rect relative to `.shell-nav`.
   // `getBoundingClientRect()` on both elements at the same tick keeps
@@ -430,7 +424,6 @@ export function Shell({ children }: { children: ComponentChildren }) {
           <SettingsMenu themeKey={THEME_KEY} motionKey={MOTION_KEY}>
             <HideDebugSetting />
             <ExpandDetailsSetting />
-            <SolidBackgroundsSetting storageKey={SOLID_KEY} />
           </SettingsMenu>
           <LinksMenu />
           <UserMenu />