diff --git a/packages/opencode/src/cli/cmd/tui/context/theme.tsx b/packages/opencode/src/cli/cmd/tui/context/theme.tsx
index 5c26d461e58c..0e346f2cfa73 100644
--- a/packages/opencode/src/cli/cmd/tui/context/theme.tsx
+++ b/packages/opencode/src/cli/cmd/tui/context/theme.tsx
@@ -78,9 +78,11 @@ type ColorValue = HexColor | RefName | Variant | RGBA
 export type ThemeJson = {
   $schema?: string
   defs?: Record<string, HexColor | RefName>
-  theme: Omit<Record<ThemeColor, ColorValue>, "selectedListItemText" | "backgroundMenu"> & {
+  theme: Omit<Record<ThemeColor, ColorValue>, "selectedListItemText" | "backgroundMenu" | "backgroundDialogOverlay" | "backgroundSidebarOverlay"> & {
     selectedListItemText?: ColorValue
     backgroundMenu?: ColorValue
+    backgroundDialogOverlay?: ColorValue
+    backgroundSidebarOverlay?: ColorValue
     thinkingOpacity?: number
   }
 }
@@ -222,7 +224,7 @@ export function resolveTheme(theme: ThemeJson, mode: "dark" | "light") {
 
   const resolved = Object.fromEntries(
     Object.entries(theme.theme)
-      .filter(([key]) => key !== "selectedListItemText" && key !== "backgroundMenu" && key !== "thinkingOpacity")
+      .filter(([key]) => key !== "selectedListItemText" && key !== "backgroundMenu" && key !== "backgroundDialogOverlay" && key !== "backgroundSidebarOverlay" && key !== "thinkingOpacity")
       .map(([key, value]) => {
         return [key, resolveColor(value as ColorValue)]
       }),
@@ -245,6 +247,20 @@ export function resolveTheme(theme: ThemeJson, mode: "dark" | "light") {
     resolved.backgroundMenu = resolved.backgroundElement
   }
 
+  // Handle backgroundDialogOverlay - optional with fallback to semi-transparent black
+  if (theme.theme.backgroundDialogOverlay !== undefined) {
+    resolved.backgroundDialogOverlay = resolveColor(theme.theme.backgroundDialogOverlay)
+  } else {
+    resolved.backgroundDialogOverlay = RGBA.fromInts(0, 0, 0, 150)
+  }
+
+  // Handle backgroundSidebarOverlay - optional with fallback to semi-transparent black
+  if (theme.theme.backgroundSidebarOverlay !== undefined) {
+    resolved.backgroundSidebarOverlay = resolveColor(theme.theme.backgroundSidebarOverlay)
+  } else {
+    resolved.backgroundSidebarOverlay = RGBA.fromInts(0, 0, 0, 70)
+  }
+
   // Handle thinkingOpacity - optional with default of 0.6
   const thinkingOpacity = theme.theme.thinkingOpacity ?? 0.6
 
@@ -575,6 +591,8 @@ function generateSystem(colors: TerminalColors, mode: "dark" | "light"): ThemeJs
       backgroundPanel: grays[2],
       backgroundElement: grays[3],
       backgroundMenu: grays[3],
+      backgroundDialogOverlay: transparent,
+      backgroundSidebarOverlay: transparent,
 
       // Border colors
       borderSubtle: grays[6],
diff --git a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
index 8855338d1d4b..02ad87ffe388 100644
--- a/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
+++ b/packages/opencode/src/cli/cmd/tui/routes/session/index.tsx
@@ -1221,7 +1221,7 @@ export function Session() {
                 right={0}
                 bottom={0}
                 alignItems="flex-end"
-                backgroundColor={RGBA.fromInts(0, 0, 0, 70)}
+                backgroundColor={theme.backgroundSidebarOverlay}
               >
                 <Sidebar sessionID={route.sessionID} />
               </box>
diff --git a/packages/opencode/src/cli/cmd/tui/ui/dialog.tsx b/packages/opencode/src/cli/cmd/tui/ui/dialog.tsx
index a5da735f6556..798e3a48db40 100644
--- a/packages/opencode/src/cli/cmd/tui/ui/dialog.tsx
+++ b/packages/opencode/src/cli/cmd/tui/ui/dialog.tsx
@@ -1,7 +1,7 @@
 import { useKeyboard, useRenderer, useTerminalDimensions } from "@opentui/solid"
 import { batch, createContext, Show, useContext, type JSX, type ParentProps } from "solid-js"
 import { useTheme } from "@tui/context/theme"
-import { MouseButton, Renderable, RGBA } from "@opentui/core"
+import { MouseButton, Renderable } from "@opentui/core"
 import { createStore } from "solid-js/store"
 import { useToast } from "./toast"
 import { Flag } from "@opencode-ai/core/flag/flag"
@@ -44,7 +44,7 @@ export function Dialog(
       paddingTop={dimensions().height / 4}
       left={0}
       top={0}
-      backgroundColor={RGBA.fromInts(0, 0, 0, 150)}
+      backgroundColor={theme.backgroundDialogOverlay}
     >
       <box
         onMouseUp={(e) => {
diff --git a/packages/opencode/test/cli/tui/theme-store.test.ts b/packages/opencode/test/cli/tui/theme-store.test.ts
index 9ebfc4320ed5..fbf60e7e7bfc 100644
--- a/packages/opencode/test/cli/tui/theme-store.test.ts
+++ b/packages/opencode/test/cli/tui/theme-store.test.ts
@@ -49,3 +49,19 @@ test("resolveTheme rejects circular color refs", () => {
 
   expect(() => resolveTheme(item, "dark")).toThrow("Circular color reference")
 })
+
+test("resolveTheme uses default for overlay backgrounds when not specified", () => {
+  const item = structuredClone(DEFAULT_THEMES.opencode)
+  const resolved = resolveTheme(item, "dark")
+  expect(resolved.backgroundDialogOverlay.a).toBeCloseTo(150 / 255, 2)
+  expect(resolved.backgroundSidebarOverlay.a).toBeCloseTo(70 / 255, 2)
+})
+
+test("resolveTheme uses custom overlay background values", () => {
+  const item = structuredClone(DEFAULT_THEMES.opencode)
+  item.theme.backgroundDialogOverlay = "#ff0000"
+  item.theme.backgroundSidebarOverlay = "#0000ff"
+  const resolved = resolveTheme(item, "dark")
+  expect(resolved.backgroundDialogOverlay.r).toEqual(1)
+  expect(resolved.backgroundSidebarOverlay.b).toEqual(1)
+})
diff --git a/packages/opencode/test/fixture/tui-plugin.ts b/packages/opencode/test/fixture/tui-plugin.ts
index 26913222e894..f3887039e002 100644
--- a/packages/opencode/test/fixture/tui-plugin.ts
+++ b/packages/opencode/test/fixture/tui-plugin.ts
@@ -38,6 +38,8 @@ function themeCurrent(): HostPluginApi["theme"]["current"] {
     backgroundPanel: h,
     backgroundElement: i,
     backgroundMenu: i,
+    backgroundDialogOverlay: RGBA.fromInts(0, 0, 0, 150),
+    backgroundSidebarOverlay: RGBA.fromInts(0, 0, 0, 70),
     border: j,
     borderActive: c,
     borderSubtle: i,
diff --git a/packages/plugin/src/tui.ts b/packages/plugin/src/tui.ts
index 1c57a71ab315..4824d42b6e8f 100644
--- a/packages/plugin/src/tui.ts
+++ b/packages/plugin/src/tui.ts
@@ -203,6 +203,8 @@ export type TuiThemeCurrent = {
   readonly backgroundPanel: RGBA
   readonly backgroundElement: RGBA
   readonly backgroundMenu: RGBA
+  readonly backgroundDialogOverlay: RGBA
+  readonly backgroundSidebarOverlay: RGBA
   readonly border: RGBA
   readonly borderActive: RGBA
   readonly borderSubtle: RGBA