[document] 메인페이지/task/로그인화면 수정

- 변경 전
<img width="596" alt="스크린샷 2022-07-19 오후 9 10 22" src="https://user-images.githubusercontent.com/24482602/179749163-05a5da0e-e00c-4ac4-9feb-187e32d1911c.png">

- 변경 후
<img width="665" alt="스크린샷 2022-07-19 오후 9 21 48" src="https://user-images.githubusercontent.com/24482602/179749247-f0712001-30e0-4fd8-8cb6-07f733afc21b.png">

