Background-remove the screenshot for dark mode (#4544)

TL-DR: Minor change. As in title. 

NOTE: 
- You cannot see the change since my fork still references the photo in
this main repo. I just use DevTools to visualize it.
- I used photoshop, and I can't quite match the drop shadow of Tailwind
CSS. But, it is more than close enough.

---

Before: 

<img width="670" alt="{0EE1F639-7B35-4622-8F3F-014F9BDE2B8F}"
src="https://github.com/user-attachments/assets/c6b32b80-7743-41a6-86b9-0b8b917e65be"
/>


After: 

<img width="470" alt="{D5324BB5-72D1-4608-87D8-7EB9B6E6887C}"
src="https://github.com/user-attachments/assets/f2bde826-5ca0-40bf-bdb9-40594f8ee641"
/>