fill.css

.html-fill-container {
  display: flex;
  flex-direction: column;
  /* Prevent the container from expanding vertically or horizontally beyond its
     parent's constraints. */
  min-height: 0;
  min-width: 0;
}
.html-fill-container > .html-fill-item {
  /* Fill items can grow and shrink freely within
     available vertical space in fillable container */
  flex: 1 1 auto;
  min-height: 0;
  min-width: 0;
}
.html-fill-container > :not(.html-fill-item) {
  /* Prevent shrinking or growing of non-fill items */
  flex: 0 0 auto;
}