postcss-grid-fluid

@gf {               /* default values */
  width: 1;         /* blob default width */
  gutter: 1.5rem;   /* gutter width */
  display: flex;    /* float or flex */
}

/* Does not output anything. */

.my-class {
  gf: row 1.5rem;
}

.my-class {
  clear: both;
  margin-right: calc(-1 * 1.5rem);
  display: flex;
  flex-flow: row wrap;
  align-items: flex-start;
  align-content: flex-start;
}

.my-class::after {
  content: "";
  display: table;
  clear: both;
}

.my-class {
  gf: blob 1/3 1.5rem flex;
}

.my-class {
  margin-right: 1.5rem;
  flex: 0 1 calc(33.3336% - 1.5rem);
}