diff --git a/src/App.tsx b/src/App.tsx
index 4782f5bc..b79b3831 100644
--- a/src/App.tsx
+++ b/src/App.tsx
@@ -6,6 +6,7 @@ import { getFirebaseRecipe, jsonToString } from "./utils/recipeLoader";
 import { getSubmitPackingUrl, JOB_STATUS } from "./constants/aws";
 import { FIRESTORE_FIELDS } from "./constants/firebase";
 import {
+    useCurrentRecipeData,
     useJobId,
     useJobLogs,
     useOutputsDirectory,
@@ -33,6 +34,7 @@ function App() {
     const setPackingResults = useSetPackingResults();
     const runTime = useRunTime();
     const outputDir = useOutputsDirectory();
+    const edits = useCurrentRecipeData()?.edits || {};
 
     let start = 0;
 
@@ -143,6 +145,7 @@ function App() {
                 resultUrl: localJobStatus.result_path,
                 runTime: range,
                 outputDir: localJobStatus.outputs_directory,
+                edits: edits,
             });
         } else if (localJobStatus.status == JOB_STATUS.FAILED) {
             setPackingResults({
@@ -151,6 +154,7 @@ function App() {
                 resultUrl: "",
                 runTime: range,
                 outputDir: "",
+                edits: {}
             });
         }
     };
diff --git a/src/components/PackingInput/index.tsx b/src/components/PackingInput/index.tsx
index a2de51da..6ed61bd6 100644
--- a/src/components/PackingInput/index.tsx
+++ b/src/components/PackingInput/index.tsx
@@ -9,6 +9,7 @@ import {
     useCurrentRecipeObject,
     useInputOptions,
     useLoadInputOptions,
+    useIsLoading,
 } from "../../state/store";
 import Dropdown from "../Dropdown";
 import JSONViewer from "../JSONViewer";
@@ -36,6 +37,7 @@ const PackingInput = (props: PackingInputProps): JSX.Element => {
     const selectedRecipeId = useSelectedRecipeId();
     const recipeObj = useCurrentRecipeObject();
     const inputOptions = useInputOptions();
+    const isLoading = useIsLoading();
 
     const loadInputOptions = useLoadInputOptions();
     const loadAllRecipes = useLoadAllRecipes();
@@ -73,7 +75,7 @@ const PackingInput = (props: PackingInputProps): JSX.Element => {
     const loadingText = <div className="recipe-select">Loading...</div>;
 
     // No recipe or dropdown options to load
-    if (!recipeObj && !inputOptions[selectedRecipeId]) {
+    if (isLoading) {
         return loadingText;
     }
 
diff --git a/src/components/Viewer/index.tsx b/src/components/Viewer/index.tsx
index 8a2dc79d..bf103991 100644
--- a/src/components/Viewer/index.tsx
+++ b/src/components/Viewer/index.tsx
@@ -1,15 +1,65 @@
+import { useEffect, useRef, useState } from "react";
+import { LoadingOutlined } from "@ant-design/icons";
 import { SIMULARIUM_EMBED_URL } from "../../constants/urls";
-import { useResultUrl } from "../../state/store";
+import { useIsLoading, useIsModified, useIsPacking, useResultUrl } from "../../state/store";
 import "./style.css";
 
 const Viewer = (): JSX.Element => {
     const resultUrl = useResultUrl();
+    const isLoadingGlobally = useIsLoading();
+    const isPacking = useIsPacking();
+    const isModified = useIsModified();
+
+  const iframeSrc = resultUrl ? `${SIMULARIUM_EMBED_URL}${resultUrl}` : "";
+
+  const lastSrcRef = useRef<string>("");
+  const [isLoadingIframe, setIsLoadingIframe] = useState(false);
+
+    useEffect(() => {
+        if (!iframeSrc) return;
+        if (iframeSrc === lastSrcRef.current) return;
+
+        lastSrcRef.current = iframeSrc;
+        setIsLoadingIframe(true);
+    }, [iframeSrc]);
+
+
+  const isLoading =
+      isLoadingGlobally || isLoadingIframe || !iframeSrc;
+
+    const overlayText = isPacking
+        ? "Running..."
+        : isLoading
+        ? "Loading..."
+        : isModified
+        ? "Re-run packing to view result"
+        : "";
+    
+    const activeState = isLoading || isPacking;
+    const showOverlay = activeState || isModified;
+
     return (
         <div className="viewer-container">
-            <iframe
-                className="simularium-embed"
-                src={`${SIMULARIUM_EMBED_URL}${resultUrl}`}
-            />
+            {iframeSrc && (
+                <iframe
+                    key={iframeSrc}
+                    className="simularium-embed"
+                    src={iframeSrc}
+                    onLoad={() => setIsLoadingIframe(false)}
+                />
+            )}
+            {showOverlay && (
+                <div className="viewer-overlay">
+                    <div
+                        className={`overlay-content ${
+                            activeState ? "active" : ""
+                        }`}
+                    >
+                        {activeState && <LoadingOutlined />}
+                        <p>{overlayText}</p>
+                    </div>
+                </div>
+            )}
         </div>
     );
 };
diff --git a/src/components/Viewer/style.css b/src/components/Viewer/style.css
index 25ca27d7..1e7cb218 100644
--- a/src/components/Viewer/style.css
+++ b/src/components/Viewer/style.css
@@ -1,10 +1,44 @@
 .viewer-container {
+    background-color: black;
     width: 100%;
     height: 100%;
+    position: relative;
 }
 
 .simularium-embed {
+    background-color: black;
     width: 100%;
     height: 100%;
     border: 1px solid black;
 }
+
+.viewer-overlay {
+    position: absolute;
+    top: 0;
+    left: 0;
+    width: 100%;
+    height: 100%;
+    background-color: #DCDDE5;
+    display: flex;
+    align-items: center;
+    justify-content: center;
+    z-index: 10;
+}
+
+.overlay-content {
+    color: #989898;
+    font-size: 32px;
+    text-align: center;
+}
+
+.overlay-content.active {
+    color: #468ADE;
+}
+
+.dark-theme .viewer-overlay {
+    background-color: #2C2F38;
+}
+
+.dark-theme .overlay-content.active {
+    color: #8b91ff;
+}
diff --git a/src/state/constants.ts b/src/state/constants.ts
index 46418079..9bb1fec3 100644
--- a/src/state/constants.ts
+++ b/src/state/constants.ts
@@ -8,4 +8,5 @@ export const EMPTY_PACKING_RESULT: PackingResult = Object.freeze({
     resultUrl: "",
     runTime: 0,
     outputDir: "",
+    edits: {},
 });
diff --git a/src/state/store.ts b/src/state/store.ts
index 48382aed..2eba5b34 100644
--- a/src/state/store.ts
+++ b/src/state/store.ts
@@ -273,6 +273,20 @@ export const useFieldsToDisplay = () =>
 export const useRecipes = () => useRecipeStore((s) => s.recipes);
 export const usePackingResults = () => useRecipeStore((s) => s.packingResults);
 
+export const useIsLoading = () => {
+    const recipeObj = useCurrentRecipeData();
+    const selectedRecipeId = useSelectedRecipeId();
+    const inputOptions = useInputOptions();
+    return !recipeObj && !inputOptions[selectedRecipeId];
+};
+
+export const useIsModified = () => {
+    const recipeObj = useCurrentRecipeData();
+    const packingResults = useCurrentPackingResult();
+    if (!recipeObj || !packingResults) return false;
+    return !isEqual(recipeObj.edits, packingResults.edits);
+};
+
 export const useCurrentRecipeObject = () => {
     const recipe = useCurrentRecipeData();
     return recipe
diff --git a/src/style/themeRoot.tsx b/src/style/themeRoot.tsx
index b835a577..3b3309b8 100644
--- a/src/style/themeRoot.tsx
+++ b/src/style/themeRoot.tsx
@@ -18,7 +18,9 @@ export function ThemeRoot({ children }: { children: React.ReactNode }) {
 
     return (
         <ConfigProvider theme={isDark ? darkTheme : lightTheme}>
-            {children}
+            <div className={isDark ? "dark-theme" : "light-theme"}>
+                {children}
+            </div>
         </ConfigProvider>
     );
 }
\ No newline at end of file
diff --git a/src/test/store.test.ts b/src/test/store.test.ts
index 34980ff8..24de1040 100644
--- a/src/test/store.test.ts
+++ b/src/test/store.test.ts
@@ -165,6 +165,7 @@ test("setPackingResults updates packing results for current recipe", async () =>
         resultUrl: "http://example.com/result",
         runTime: 120,
         outputDir: "/output/dir",
+        edits: {}
     };
 
     act(() => {
diff --git a/src/types/index.ts b/src/types/index.ts
index 64f73cc1..1d427d8f 100644
--- a/src/types/index.ts
+++ b/src/types/index.ts
@@ -46,6 +46,7 @@ export type PackingResult = {
     resultUrl: string;
     runTime: number;
     outputDir: string;
+    edits: Record<string, string | number>;
 };
 
 export type EditableField = {