diff --git a/ui/src/components/DocumentAnnotationLayer.test.tsx b/ui/src/components/DocumentAnnotationLayer.test.tsx
new file mode 100644
index 00000000000..4e49a5424ef
--- /dev/null
+++ b/ui/src/components/DocumentAnnotationLayer.test.tsx
@@ -0,0 +1,99 @@
+// @vitest-environment jsdom
+
+import { act } from "react";
+import { createRoot, type Root } from "react-dom/client";
+import { afterEach, beforeEach, describe, expect, it, vi } from "vitest";
+import { DocumentAnnotationLayer } from "./DocumentAnnotationLayer";
+
+const mockRangesForNormalizedSpan = vi.hoisted(() => vi.fn());
+
+vi.mock("@/lib/document-annotation-selection", () => ({
+  buildAnchorFromContainerSelection: vi.fn(),
+  getContainerTextOffset: vi.fn(),
+  rangesForNormalizedSpan: mockRangesForNormalizedSpan,
+}));
+
+// eslint-disable-next-line @typescript-eslint/no-explicit-any
+(globalThis as any).IS_REACT_ACT_ENVIRONMENT = true;
+
+function makeRect(left: number, top: number, width: number, height: number): DOMRect {
+  return {
+    x: left,
+    y: top,
+    left,
+    top,
+    right: left + width,
+    bottom: top + height,
+    width,
+    height,
+    toJSON: () => ({}),
+  } as DOMRect;
+}
+
+describe("DocumentAnnotationLayer", () => {
+  let container: HTMLDivElement;
+  let rectSpy: ReturnType<typeof vi.spyOn>;
+  let root: Root | null = null;
+
+  beforeEach(() => {
+    container = document.createElement("div");
+    document.body.appendChild(container);
+    mockRangesForNormalizedSpan.mockReturnValue([
+      {
+        getClientRects: () => [makeRect(8, 12, 80, 18)],
+      },
+    ]);
+    rectSpy = vi.spyOn(HTMLElement.prototype, "getBoundingClientRect").mockReturnValue(makeRect(0, 0, 400, 300));
+  });
+
+  afterEach(() => {
+    if (root) {
+      act(() => root?.unmount());
+      root = null;
+    }
+    rectSpy.mockRestore();
+    container.remove();
+    vi.clearAllMocks();
+  });
+
+  it("uses solid yellow backgrounds for annotation highlights in light and dark themes", async () => {
+    const body = document.createElement("div");
+    body.textContent = "Annotated body text.";
+    root = createRoot(container);
+
+    await act(async () => {
+      root?.render(
+        <DocumentAnnotationLayer
+          containerRef={{ current: body }}
+          markdown="Annotated body text."
+          threads={[
+            { id: "active", selectedText: "Annotated", status: "open", anchorState: "active" },
+            { id: "focused", selectedText: "body", status: "open", anchorState: "active" },
+            { id: "stale", selectedText: "text", status: "open", anchorState: "stale" },
+            { id: "resolved", selectedText: "body text", status: "resolved", anchorState: "active" },
+          ]}
+          focusedThreadId="focused"
+          onThreadFocus={vi.fn()}
+          pendingAnchor={null}
+          onPendingAnchorChange={vi.fn()}
+          onRequestComment={vi.fn()}
+          hideResolved={false}
+        />,
+      );
+      await new Promise((resolve) => window.requestAnimationFrame(resolve));
+    });
+
+    const highlights = Array.from(container.querySelectorAll(".paperclip-doc-annotation-highlight"));
+    expect(highlights).toHaveLength(4);
+
+    for (const highlight of highlights) {
+      const backgroundClasses = Array.from(highlight.classList).filter((className) =>
+        /^(dark:|hover:|dark:hover:)?bg-yellow-\d+$/.test(className)
+        || /^(dark:|hover:|dark:hover:)?bg-yellow-\d+\//.test(className),
+      );
+      expect(backgroundClasses.some((className) => className.includes("/"))).toBe(false);
+      expect(backgroundClasses.some((className) => className.startsWith("bg-yellow-"))).toBe(true);
+      expect(backgroundClasses.some((className) => className.startsWith("dark:bg-yellow-"))).toBe(true);
+    }
+  });
+});
diff --git a/ui/src/components/DocumentAnnotationLayer.tsx b/ui/src/components/DocumentAnnotationLayer.tsx
index 1c4e423b44b..98b67f70bef 100644
--- a/ui/src/components/DocumentAnnotationLayer.tsx
+++ b/ui/src/components/DocumentAnnotationLayer.tsx
@@ -268,12 +268,12 @@ export function DocumentAnnotationLayer({
                 "paperclip-doc-annotation-highlight pointer-events-auto absolute cursor-pointer rounded-none transition-colors",
                 // base box treatment (replaces the previous baseline border)
                 isResolved
-                  ? "bg-yellow-300/25 outline outline-1 outline-dashed outline-offset-0 outline-yellow-700/45 hover:bg-yellow-300/35 dark:bg-yellow-300/18 dark:outline-yellow-200/45"
+                  ? "bg-yellow-100 outline outline-1 outline-dashed outline-offset-0 outline-yellow-700/45 hover:bg-yellow-200 dark:bg-yellow-700 dark:outline-yellow-200/45 dark:hover:bg-yellow-600"
                   : isStale
-                    ? "bg-yellow-300/35 outline outline-2 outline-dashed outline-offset-0 outline-yellow-700/65 hover:bg-yellow-300/45 dark:bg-yellow-300/24 dark:outline-yellow-200/70"
+                    ? "bg-yellow-200 outline outline-2 outline-dashed outline-offset-0 outline-yellow-700/65 hover:bg-yellow-300 dark:bg-yellow-600 dark:outline-yellow-200/70 dark:hover:bg-yellow-500"
                     : isFocused
-                      ? "bg-yellow-300/55 outline outline-2 outline-offset-0 outline-yellow-700/85 shadow-[0_0_0_1px_var(--color-background)] dark:bg-yellow-300/35 dark:outline-yellow-200/85"
-                      : "bg-yellow-300/40 hover:bg-yellow-300/55 dark:bg-yellow-300/24 dark:hover:bg-yellow-300/34",
+                      ? "bg-yellow-300 outline outline-2 outline-offset-0 outline-yellow-700/85 shadow-[0_0_0_1px_var(--color-background)] hover:bg-yellow-300 dark:bg-yellow-500 dark:outline-yellow-200/85 dark:hover:bg-yellow-400"
+                      : "bg-yellow-200 hover:bg-yellow-300 dark:bg-yellow-600 dark:hover:bg-yellow-500",
               )}
               style={{
                 top: rect.top,