vi · vb
The viewport measured by the axes of writing, not the sides of the screen.
One vi is 1% of the viewport along the inline axis — the axis text runs along — and one vb, 1% along the block axis, where paragraphs stack. In English and Portuguese, vi coincides with vw and vb with vh.
The coincidence ends when writing-mode turns: in a vertical Japanese or Mongolian layout the axes swap places, and a sheet written in vi and vb rotates along without touching a line. They are the viewport's logical units, partners of inline-size and block-size.
.faixa {
inline-size: 40vi;
margin-block: 2vb;
}