.b-grid>I {
background: linear-gradient(to bottom,#c7c7c7,#c7c7c7 50%,transparent 50%,transparent) 0 0/1px 2px repeat-y;
}
.b-grid._inv>I {
background: linear-gradient(to bottom,#fff,#fff 50%,transparent 50%,transparent) 0 0/1px 2px repeat-y;
}
.b-grid>I+I {
left: 30rem;
}
.b-grid>I+I+I {
left: 60rem;
}