🎨 Palette: Improve Button loading state accessibility

- Add `aria-busy` attribute to Button when loading.
- Refactor Button rendering to keep children in DOM (visually hidden) instead of unmounting.
- Fix layout shift regression by replicating flex properties in content wrapper.
- Move inline styles to CSS modules.
- Add tests for loading state accessibility.

Co-authored-by: ragusa-it <196988693+ragusa-it@users.noreply.github.com>

.Jules/palette.md

@@ -1,3 +1,7 @@
 ## 2024-05-24 - Accessible Input Validation
 **Learning:** React 19 renders `aria-invalid={false}` as `aria-invalid="false"`, unlike older versions which might have omitted it. Explicitly handling this in tests is crucial. Also, ensuring DOM cleanup (`cleanup()`) in `afterEach` is vital when testing similar components with same labels across tests to avoid "finding the wrong element" false positives/negatives.
 **Action:** Always include `afterEach(() => cleanup())` in `vitest` setup for DOM tests, and expect `aria-invalid="false"` (or explicitly handle `undefined` if omission is desired) when testing valid states in React 19.
+
+## 2024-05-24 - Accessible Loading Buttons
+**Learning:** Replacing button text with a spinner destroys the accessible name.
+**Action:** Use `aria-busy="true"`, keep children in DOM (visually hidden via opacity/class), and overlay spinner absolutely. Ensure wrapper element replicates flex layout (gap/alignment) to prevent layout shifts.

src/components/ui/Button.module.css

@@ -1,5 +1,6 @@
 .button {
   display: inline-flex;
+  position: relative;
   align-items: center;
   justify-content: center;
   gap: var(--space-sm);
@@ -80,3 +81,23 @@
     transform: rotate(360deg);
   }
 }
+
+.content {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  gap: var(--space-sm);
+  transition: opacity 0.2s;
+}
+
+.contentHidden {
+  opacity: 0;
+}
+
+.loaderWrapper {
+  position: absolute;
+  inset: 0;
+  display: flex;
+  align-items: center;
+  justify-content: center;
+}

src/components/ui/Button.tsx

@@ -24,14 +24,18 @@ export function Button({
       type={type}
       className={`${styles.button} ${styles[variant]} ${styles[size]} ${className || ''}`}
       disabled={disabled || isLoading}
+      aria-busy={isLoading}
       whileHover={{ scale: 1.02 }}
       whileTap={{ scale: 0.98 }}
       {...props}
     >
-      {isLoading ? (
+      <span className={`${styles.content} ${isLoading ? styles.contentHidden : ''}`}>
+        {children}
+      </span>
+      {isLoading && (
+        <span className={styles.loaderWrapper} aria-hidden="true">
           <span className={styles.loader} />
-      ) : (
-        children
+        </span>
       )}
     </motion.button>
   );

src/components/ui/__tests__/Button.test.tsx

@@ -19,4 +19,13 @@ describe('Button', () => {
     const button = screen.getByTestId('custom-button');
     expect(button).toBeTruthy();
   });
+
+  it('renders loading state correctly', () => {
+    render(<Button isLoading>Submit</Button>);
+    const button = screen.getByRole('button', { name: /submit/i }) as HTMLButtonElement;
+    expect(button.getAttribute('aria-busy')).toBe('true');
+    expect(button.disabled).toBe(true);
+    // Verify text is present (opacity: 0 doesn't remove from DOM)
+    expect(screen.getByText('Submit')).toBeTruthy();
+  });
 });