Add dark theme

[jo-elimu]

Description

Add dark theme to the UI.

Note

The Materialize library needs to be upgraded before implementing this change.

Why?

Reduce eyestrain for content creators.

---

• Depends on Upgrade Materialize from version 0.100.2 to 1.0.0 #1451

---

elimu.ai's mission is to build innovative learning software that empowers out-of-school children to teach themselves basic reading📖, writing✍🏽 and math🔢 within 6 months.