diff --git a/apps/readest-app/src/__tests__/styles/eink-dropdown-toggle.test.ts b/apps/readest-app/src/__tests__/styles/eink-dropdown-toggle.test.ts
new file mode 100644
index 00000000..8f0fde9d
--- /dev/null
+++ b/apps/readest-app/src/__tests__/styles/eink-dropdown-toggle.test.ts
@@ -0,0 +1,40 @@
+import { describe, it, expect } from 'vitest';
+import { readFileSync } from 'fs';
+import { resolve } from 'path';
+
+/**
+ * Regression guard for issue #4435 (button display under the e-ink screen).
+ *
+ * The Android "Choose New Folder" selector in the Change Data Location dialog is
+ * a `Dropdown` whose toggle carries `dropdown-toggle ... btn btn-ghost
+ * btn-outline`. Under `[data-eink='true']`, globals.css inverts `.btn-outline`
+ * to a solid fill (`background: base-content`, `color: base-100`). The dedicated
+ * `[data-eink='true'] .dropdown-toggle` rule then neutralizes the background
+ * back to transparent — but it used to leave the inverted white (`base-100`)
+ * text untouched, so the label became white-on-transparent (white-on-white):
+ * an empty-looking outlined box.
+ *
+ * Invariant: the e-ink `.dropdown-toggle` rule must reset BOTH the background
+ * (transparent) AND the text color (base-content), so a transparent-background
+ * toggle keeps a legible dark label regardless of any fill class it also wears.
+ */
+describe('e-ink dropdown-toggle legibility', () => {
+  const css = readFileSync(resolve(process.cwd(), 'src/styles/globals.css'), 'utf8');
+
+  const block = (() => {
+    const selector = "[data-eink='true'] .dropdown-toggle";
+    const start = css.indexOf(selector);
+    expect(start, `expected globals.css to define ${selector}`).toBeGreaterThanOrEqual(0);
+    const open = css.indexOf('{', start);
+    const close = css.indexOf('}', open);
+    return css.slice(open + 1, close);
+  })();
+
+  it('neutralizes the toggle background to transparent', () => {
+    expect(block).toMatch(/background-color:\s*theme\('colors\.transparent'\)/);
+  });
+
+  it('resets the toggle text color to base-content so it stays legible', () => {
+    expect(block).toMatch(/color:\s*theme\('colors\.base-content'\)/);
+  });
+});
diff --git a/apps/readest-app/src/styles/globals.css b/apps/readest-app/src/styles/globals.css
index 329c1e2a..06fc0fe3 100644
--- a/apps/readest-app/src/styles/globals.css
+++ b/apps/readest-app/src/styles/globals.css
@@ -604,6 +604,11 @@ input[type='range'].slider-input {
 
 [data-eink='true'] .dropdown-toggle {
   background-color: theme('colors.transparent') !important;
+  /* A toggle that also carries a fill class (e.g. btn-outline) gets its label
+     inverted to base-100 by the rule above; with the background neutralized to
+     transparent that leaves white-on-white. Keep the text base-content so the
+     label stays legible (issue #4435). */
+  color: theme('colors.base-content') !important;
 }
 
 [data-eink='true'] .opds-navigation .card {