diff --git a/src/components/output/custom-els/MultiPanel/index.ts b/src/components/compress/custom-els/MultiPanel/index.ts
similarity index 82%
rename from src/components/output/custom-els/MultiPanel/index.ts
rename to src/components/compress/custom-els/MultiPanel/index.ts
index 95a06dcd..3a5cef8f 100644
--- a/src/components/output/custom-els/MultiPanel/index.ts
+++ b/src/components/compress/custom-els/MultiPanel/index.ts
@@ -1,8 +1,10 @@
-import './styles.css';
+import * as style from './styles.css';
+
+const openOneOnlyAttr = 'open-one-only';
 
 function getClosestHeading(el: Element) {
   const closestEl = el.closest('multi-panel > *');
-  if (closestEl && closestEl.classList.contains('panel-heading')) {
+  if (closestEl && closestEl.classList.contains(style.panelHeading)) {
     return closestEl;
   }
   return undefined;
@@ -14,6 +16,7 @@ function getClosestHeading(el: Element) {
  * and odd index element becomes the expandable content.
  */
 export default class MultiPanel extends HTMLElement {
+  static get observedAttributes() { return [openOneOnlyAttr]; }
 
   constructor() {
     super();
@@ -31,12 +34,18 @@ export default class MultiPanel extends HTMLElement {
     this._childrenChange();
   }
 
+  attributeChangedCallback(name: string, oldValue: string | null, newValue: string | null) {
+    if (name === openOneOnlyAttr && newValue === null) {
+      // TODO
+    }
+  }
+
   // Click event handler
   private _onClick(event: MouseEvent) {
     const el = event.target as Element;
     const heading = getClosestHeading(el);
     if (!heading) return;
-    this._expand(heading);
+    this._toggle(heading);
   }
 
   // KeyDown event handler
@@ -77,7 +86,7 @@ export default class MultiPanel extends HTMLElement {
       case 'Enter':
       case ' ':
       case 'Spacebar':
-        this._expand(heading);
+        this._toggle(heading);
         break;
 
       // Any other key press is ignored and passed back to the browser.
@@ -93,7 +102,7 @@ export default class MultiPanel extends HTMLElement {
     }
   }
 
-  private _expand(heading: Element) {
+  private _toggle(heading: Element) {
     if (!heading) return;
     const content = heading.nextElementSibling;
 
@@ -105,11 +114,21 @@ export default class MultiPanel extends HTMLElement {
       content.removeAttribute('expanded');
       content.setAttribute('aria-expanded', 'false');
     } else {
+      if (this.openOneOnly) this._closeAll();
       content.setAttribute('expanded', '');
       content.setAttribute('aria-expanded', 'true');
     }
   }
 
+  private _closeAll(): void {
+    const els = [...this.children].filter(el => el.matches('[expanded]'));
+
+    for (const el of els) {
+      el.removeAttribute('expanded');
+      el.setAttribute('aria-expanded', 'false');
+    }
+  }
+
   // children of multi-panel should always be even number (heading/content pair)
   private _childrenChange() {
     let preserveTabIndex : boolean = false;
@@ -130,10 +149,10 @@ export default class MultiPanel extends HTMLElement {
       // When odd number of elements were inserted in the middle,
       // what was heading before may become content after the insertion.
       // Remove classes and attributes to prepare for this change.
-      heading.classList.remove('panel-content');
+      heading.classList.remove(style.panelContent);
 
-      if (content.classList.contains('panel-heading')) {
-        content.classList.remove('panel-heading');
+      if (content.classList.contains(style.panelHeading)) {
+        content.classList.remove(style.panelHeading);
       }
       if (heading.hasAttribute('expanded') && heading.hasAttribute('aria-expanded')) {
         heading.removeAttribute('expanded');
@@ -146,8 +165,8 @@ export default class MultiPanel extends HTMLElement {
       }
 
       // Assign heading and content classes
-      heading.classList.add('panel-heading');
-      content.classList.add('panel-content');
+      heading.classList.add(style.panelHeading);
+      content.classList.add(style.panelContent);
 
       // Assign ids and aria-X for heading/content pair.
       heading.id = `panel-heading-${randomId}`;
@@ -208,7 +227,7 @@ export default class MultiPanel extends HTMLElement {
   private _lastHeading() {
     // if the last element is heading, return last element
     const lastEl = this.lastElementChild as HTMLElement;
-    if (lastEl && lastEl.classList.contains('panel-heading')) {
+    if (lastEl && lastEl.classList.contains(style.panelHeading)) {
       return lastEl;
     }
     // otherwise return 2nd from the last
@@ -217,6 +236,21 @@ export default class MultiPanel extends HTMLElement {
       return lastContent.previousElementSibling as HTMLElement;
     }
   }
+
+  /**
+   * If true, only one panel can be open at once. When one opens, others close.
+   */
+  get openOneOnly() {
+    return this.hasAttribute(openOneOnlyAttr);
+  }
+
+  set openOneOnly(val: boolean) {
+    if (val) {
+      this.setAttribute(openOneOnlyAttr, '');
+    } else {
+      this.removeAttribute(openOneOnlyAttr);
+    }
+  }
 }
 
 customElements.define('multi-panel', MultiPanel);
diff --git a/src/components/compress/custom-els/MultiPanel/missing-types.d.ts b/src/components/compress/custom-els/MultiPanel/missing-types.d.ts
new file mode 100644
index 00000000..b775fa8a
--- /dev/null
+++ b/src/components/compress/custom-els/MultiPanel/missing-types.d.ts
@@ -0,0 +1,9 @@
+interface MultiPanelAttributes extends JSX.HTMLAttributes {
+  'open-one-only'?: boolean;
+}
+
+declare namespace JSX {
+  interface IntrinsicElements {
+    'multi-panel': MultiPanelAttributes;
+  }
+}
diff --git a/src/components/compress/custom-els/MultiPanel/styles.css b/src/components/compress/custom-els/MultiPanel/styles.css
new file mode 100644
index 00000000..286c5fa7
--- /dev/null
+++ b/src/components/compress/custom-els/MultiPanel/styles.css
@@ -0,0 +1,11 @@
+.panel-heading {
+  background:gray;
+}
+.panel-content {
+  height:0px;
+  overflow:scroll;
+  transition: height 1s;
+}
+.panel-content[expanded] {
+  height:auto;
+}
diff --git a/src/components/compress/index.tsx b/src/components/compress/index.tsx
index 83e4ab58..76ca993a 100644
--- a/src/components/compress/index.tsx
+++ b/src/components/compress/index.tsx
@@ -24,16 +24,15 @@ import {
     EncoderOptions,
     encoderMap,
 } from '../../codecs/encoders';
-
 import {
   PreprocessorState,
   defaultPreprocessorState,
 } from '../../codecs/preprocessors';
-
 import { decodeImage } from '../../codecs/decoders';
 import { cleanMerge, cleanSet } from '../../lib/clean-modify';
 import Processor from '../../codecs/processor';
 import { VectorResizeOptions, BitmapResizeOptions } from '../../codecs/resize/processor-meta';
+import './custom-els/MultiPanel';
 
 export interface SourceImage {
   file: File | Fileish;
@@ -397,6 +396,23 @@ export default class Compress extends Component<Props, State> {
     const [leftImage, rightImage] = images;
     const [leftImageData, rightImageData] = images.map(i => i.data);
 
+    const options = images.map((image, index) => (
+      <Options
+        loading={loading || image.loading}
+        source={source}
+        mobileView={mobileView}
+        imageIndex={index}
+        imageFile={image.file}
+        downloadUrl={image.downloadUrl}
+        preprocessorState={image.preprocessorState}
+        encoderState={image.encoderState}
+        onEncoderTypeChange={this.onEncoderTypeChange.bind(this, index)}
+        onEncoderOptionsChange={this.onEncoderOptionsChange.bind(this, index)}
+        onPreprocessorOptionsChange={this.onPreprocessorOptionsChange.bind(this, index)}
+        onCopyToOtherClick={this.onCopyToOtherClick.bind(this, index)}
+      />
+    ));
+
     return (
       <div class={style.compress}>
         <Output
@@ -407,22 +423,16 @@ export default class Compress extends Component<Props, State> {
           leftImgContain={leftImage.preprocessorState.resize.fitMethod === 'cover'}
           rightImgContain={rightImage.preprocessorState.resize.fitMethod === 'cover'}
         />
-        {images.map((image, index) => (
-          <Options
-            loading={loading || image.loading}
-            source={source}
-            mobileView={mobileView}
-            imageIndex={index}
-            imageFile={image.file}
-            downloadUrl={image.downloadUrl}
-            preprocessorState={image.preprocessorState}
-            encoderState={image.encoderState}
-            onEncoderTypeChange={this.onEncoderTypeChange.bind(this, index)}
-            onEncoderOptionsChange={this.onEncoderOptionsChange.bind(this, index)}
-            onPreprocessorOptionsChange={this.onPreprocessorOptionsChange.bind(this, index)}
-            onCopyToOtherClick={this.onCopyToOtherClick.bind(this, index)}
-          />
-        ))}
+        {mobileView
+          ? (
+            <multi-panel class={style.multiPanel} open-one-only>
+              <div>Top</div>
+              {options[0]}
+              <div>Bottom</div>
+              {options[1]}
+            </multi-panel>
+          ) : options
+        }
       </div>
     );
   }
diff --git a/src/components/compress/style.scss b/src/components/compress/style.scss
index 211e6813..23ae1061 100644
--- a/src/components/compress/style.scss
+++ b/src/components/compress/style.scss
@@ -16,3 +16,7 @@
     grid-template-rows: 100%;
   }
 }
+
+.multi-panel {
+  position: relative;
+}
diff --git a/src/components/output/custom-els/MultiPanel/styles.css b/src/components/output/custom-els/MultiPanel/styles.css
deleted file mode 100644
index 97047454..00000000
--- a/src/components/output/custom-els/MultiPanel/styles.css
+++ /dev/null
@@ -1,11 +0,0 @@
-multi-panel > .panel-heading {
-  background:gray;
-}
-multi-panel > .panel-content {
-  height:0px;
-  overflow:scroll;
-  transition: height 1s;
-}
-multi-panel > .panel-content[expanded] {
-  height:auto;
-}