px 7px 5px;
  border-style: solid;
}
rbc {
  display: ruby-base-container;
  unicode-bidi: isolate;
  font-size: 200%;
}
rtc {
  display: ruby-text-container;
  unicode-bidi: isolate;
  ruby-position: under;
}
x { display:block; width:3em; overflow:hidden; background:lightblue; }
</style>

<div>zzzzzzzzzzzz</div>
<ruby class=mbp>X<div>zzzzzzzzzzzz</div></ruby>
<grid>A<x class=mbp><rbb><div>zzzzzzzzzzzz</div></rbb></x>B</grid>
<grid>A<x class=mbp><rbb>X<div>zzzzzzzzzzzz</div></rbb></x>B</grid>
<grid>A<x><rbb