message: fix(FixedLayout): correct centering
diff: .FixedLayout {
  position: fixed;
  box-sizing: border-box;
  - left: auto;
  + left: 0;
  + right: 0;
  z-index: 3;
  + margin-left: auto;
  + margin-right: auto;
  padding-left: var(--safe-area-inset-left);
  padding-right: var(--safe-area-inset-right);
  }
  .FixedLayout--top {
  width: 100%;
  top: 0;
  - left: 0;
  }
  .FixedLayout--bottom {
  width: 100%;
  - left: 0;
  bottom: 0;
  padding-bottom: var(--safe-area-inset-bottom);
  }
  