message: feat(components): improve backtotop button appearance
diff: position: fixed !important;
  right: 1rem;
  - bottom: 4rem;
  + bottom: 8rem;
  z-index: 100;
  width: 3rem;
  height: 3rem;
  - padding: 8px;
  + padding: 0.5rem;
  border-radius: 1rem;
  - background-color: var(--white);
  + background-color: var(--c-bg, #fff);
  box-shadow: 2px 2px 10px 0 var(--card-shadow);
  color: var(--c-brand, #3eaf7c);
  color: var(--c-brand-light, #4abf8a);
  }
  + @media (max-width: hope-config.$mobile) {
  + width: 2.25rem;
  + height: 2.25rem;
  + padding: 0.25rem;
  + border-radius: 0.5rem;
  + }
  +
  svg {
  width: 100%;
  border-radius: 50%;
  