Mastery Challenges in the new mastery experience

Hi Khan Academy! Mastery Challenges need some updates in the new mastery view. First is this one, too good to ignore: add an encouraging "keep learning" message after finishing MC.

Bigger MCs: I'd love an expansion of MCs to 12 questions 6 skills, or 20 questions 10 skills. The current skill-question ratio is too small, and expanding it revives the Missions feel.

Colorful MCs: I'd also love some colorful updates to the MC box, esp. colors of LearnStorm, and super-engaging confetti when a student finishes MC.

Pre-test card in MCs: MC needs a pre-test card, just like Course Challenge and Unit Tests. This card must describe what MC is and why take it, but not mention which skills will be tested. Post-test, MC must show which skills were leveled up or down.

Quicker, 6-hour MCs: Faster reset times, like 6 hours rather than 12, helps in levelling up faster, but spaced repetition is a long-term thing: even 12 hour MCs need to be taken by students to revise ideas, but 6r ones help in quicker level ups. Regularly, then, students can take MCs to revise concepts and skills.

MCs in more courses: I'd love to see MCs in Digital SAT Math, as well as Science courses. What's the motive behind adding MCs only for Math now: can't it be a feature for all mastery-enabled courses?

Course Challenge and MCs: MCs are at just the right place, on top, but I suggest moving CCs too to the top, same place at MCs, but there's more detail. CC is the default box, in the MC's position. When MC criteria are met, MC appears instead of CC. Once MC is complete, CC appears again until the next reset of MCs.