The classes o-grid__row--divided-rows
and o-grid__row--divided-column
can be added to the grid row to put a subtle divider between rows and/or colums.
It looks better when you combine it with an equal height row.
Because of the enormous complexity involved, please don't use responsive overrides on grid sizes
Divided rows
.o-grid__box--full
.o-grid__box--half
.o-grid__box--half
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--threequarters
.o-grid__box--threequarters
.o-grid__box--quarter
.o-grid__box--third
.o-grid__box--twothirds
.o-grid__box--twothirds
.o-grid__box--third
.o-grid__box--third
.o-grid__box--third
.o-grid__box--third
<div class="o-grid">
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--full">
.o-grid__box--full
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--threequarters">
.o-grid__box--threequarters
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--threequarters">
.o-grid__box--threequarters
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--twothirds">
.o-grid__box--twothirds
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--twothirds">
.o-grid__box--twothirds
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows">
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
</div>
</div>
Divided columns
.o-grid__box--full
.o-grid__box--half
.o-grid__box--half
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--threequarters
.o-grid__box--threequarters
.o-grid__box--quarter
.o-grid__box--third
.o-grid__box--twothirds
.o-grid__box--twothirds
.o-grid__box--third
.o-grid__box--third
.o-grid__box--third
.o-grid__box--third
<div class="o-grid">
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--full">
.o-grid__box--full
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--threequarters">
.o-grid__box--threequarters
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--threequarters">
.o-grid__box--threequarters
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--twothirds">
.o-grid__box--twothirds
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--twothirds">
.o-grid__box--twothirds
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
</div>
<div class="o-grid__row o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
</div>
</div>
Divided rows and columns
.o-grid__box--full
.o-grid__box--half
.o-grid__box--half
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--half
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--quarter
.o-grid__box--threequarters
.o-grid__box--threequarters
.o-grid__box--quarter
.o-grid__box--third
.o-grid__box--twothirds
.o-grid__box--twothirds
.o-grid__box--third
.o-grid__box--third
.o-grid__box--third
.o-grid__box--third
<div class="o-grid">
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--full">
.o-grid__box--full
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--half">
.o-grid__box--half
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
<div class="o-grid__box o-grid__box--threequarters">
.o-grid__box--threequarters
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--threequarters">
.o-grid__box--threequarters
</div>
<div class="o-grid__box o-grid__box--quarter">
.o-grid__box--quarter
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--twothirds">
.o-grid__box--twothirds
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--twothirds">
.o-grid__box--twothirds
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
</div>
<div class="o-grid__row o-grid__row--divided-rows o-grid__row--divided-columns">
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
<div class="o-grid__box o-grid__box--third">
.o-grid__box--third
</div>
</div>
</div>