Each Category menu item or Tag menu item might comes with drop-down recent posts. See how it can be added.

Follow steps:

  1. Go to Appearance > Menus page and enable CSS Classes from witin Screen Options panel.

  2. Enable Categories and Tags as well.

  3. Add some of them to your menu.

  4. Put the st-mega-taxonomy-post-v-1 on CSS Classes input field.

  5. Save menu. Done.

Strict Themes