feat: add position prop to modal

src/__tests__/snapshot-tests/__snapshots__/documenter.test.ts.snap

@@ -17484,6 +17484,28 @@ render to an element under \`document.body\`.",
       "optional": true,
       "type": "HTMLElement",
     },
+    {
+      "defaultValue": "'center'",
+      "description": "Controls the vertical positioning of the modal.
+
+- \`center\` (default) - Modal is vertically centered in viewport and re-centers
+  when content height changes. Use for dialogs with static, predictable content.
+
+- \`top\` - Modal anchors at fixed distance and grows downward
+  as content expands. Use when content changes dynamically to prevent disruptive
+  vertical repositioning that causes users to lose focus.",
+      "inlineType": {
+        "name": "ModalProps.Position",
+        "type": "union",
+        "values": [
+          "center",
+          "top",
+        ],
+      },
+      "name": "position",
+      "optional": true,
+      "type": "string",
+    },
     {
       "description": "Use this property when \`getModalRoot\` is used to clean up the modal root
 element after a user closes the dialog. The function receives the return value

src/modal/__tests__/modal.test.tsx

@@ -119,6 +119,15 @@
     });
   });
 
+  describe('position property', () => {
+    it('displays correct position', () => {
+      (['center', 'top'] as ModalProps.Position[]).forEach(position => {
+        const wrapper = renderModal({ position });
+        expect(wrapper.findDialog().getElement()).toHaveClass(styles[position]);
+      });
+    });
+  });
+
   describe('dismiss on click', () => {
     it('closes the dialog when clicked on the overlay section of the container', () => {
       const onDismissSpy = jest.fn();

src/modal/index.tsx

@@ -70,14 +70,15 @@ function ModalWithAnalyticsFunnel({
   );
 }
 
-export default function Modal({ size = 'medium', ...props }: ModalProps) {
+export default function Modal({ size = 'medium', position = 'center', ...props }: ModalProps) {
   const { isInFunnel } = useFunnel();
   const analyticsMetadata = getAnalyticsMetadataProps(props as BasePropsWithAnalyticsMetadata);
   const baseComponentProps = useBaseComponent(
     'Modal',
     {
       props: {
         size,
+        position,
         disableContentPaddings: props.disableContentPaddings,
         flowType: analyticsMetadata.flowType,
       },
@@ -95,12 +96,21 @@ export default function Modal({ size = 'medium', ...props }: ModalProps) {
         analyticsMetadata={analyticsMetadata}
         baseComponentProps={baseComponentProps}
         size={size}
+        position={position}
         {...props}
       />
     );
   }
 
-  return <InternalModal size={size} {...props} {...baseComponentProps} __injectAnalyticsComponentMetadata={true} />;
+  return (
+    <InternalModal
+      size={size}
+      position={position}
+      {...props}
+      {...baseComponentProps}
+      __injectAnalyticsComponentMetadata={true}
+    />
+  );
 }
 
 applyDisplayName(Modal, 'Modal');

src/modal/interfaces.ts

@@ -30,6 +30,17 @@ export interface ModalProps extends BaseComponentProps, BaseModalProps {
    * `small` (320px), `medium` (600px), `large` (820px), `x-large` (1024px), `xx-large` (1280px).
    */
   size?: ModalProps.Size;
+  /**
+   * Controls the vertical positioning of the modal.
+   *
+   * - `center` (default) - Modal is vertically centered in viewport and re-centers
+   *   when content height changes. Use for dialogs with static, predictable content.
+   *
+   * - `top` - Modal anchors at fixed distance and grows downward
+   *   as content expands. Use when content changes dynamically to prevent disruptive
+   *   vertical repositioning that causes users to lose focus.
+   */
+  position?: ModalProps.Position;
   /**
    * Determines whether the modal is displayed on the screen. Modals are hidden by default.
    * Set this property to `true` to show them.
@@ -82,6 +93,7 @@ export interface ModalProps extends BaseComponentProps, BaseModalProps {
 
 export namespace ModalProps {
   export type Size = 'small' | 'medium' | 'large' | 'x-large' | 'xx-large' | 'max';
+  export type Position = 'center' | 'top';
 
   export interface DismissDetail {
     reason: string;

src/modal/internal.tsx

@@ -94,6 +94,7 @@ function PortaledModal({
   children,
   footer,
   disableContentPaddings,
+  position = 'center',
   onButtonClick = () => {},
   onDismiss,
   __internalRootRef,
@@ -247,7 +248,12 @@ function PortaledModal({
             style={footerHeight ? { scrollPaddingBottom: footerHeight } : undefined}
             data-awsui-referrer-id={subStepRef.current?.id || referrerId}
           >
-            <FocusLock disabled={!visible} autoFocus={true} restoreFocus={true} className={styles['focus-lock']}>
+            <FocusLock
+              disabled={!visible}
+              autoFocus={true}
+              restoreFocus={true}
+              className={clsx(styles['focus-lock'], position === 'top' && styles['position-top'])}
+            >
               <div
                 className={clsx(
                   styles.dialog,

src/modal/styles.scss

@@ -39,6 +39,10 @@ $modal-z-index: 5000;
   padding-inline: 0;
   z-index: $modal-z-index;
   pointer-events: none;
+
+  &.position-top {
+    margin-block-start: awsui.$space-s;
+  }
 }
 
 .dialog {