message: feat(components): improve backtotop button style
diff: position: fixed !important;
  right: 1rem;
  - bottom: 8rem;
  + bottom: 4rem;
  z-index: 100;
  width: 3rem;
  height: 3rem;
  }
  @media (max-width: hope-config.$mobile) {
  + bottom: 8rem;
  width: 2.25rem;
  height: 2.25rem;
  padding: 0.25rem;
  