Isolation and Bleed in Susy

A few new features have landed in Susy 1.0.7, even as we work on more integrated syntaxes for 2.0.


Sub-pixel rounding has always been a problem for fluid design. Susy takes care of the most egregious layout-breaking cases, but there is no way to entirely eliminate the problem.

John Albin Wilkins has a demo of the problem, as well as a proposed solution. He hasn’t eliminated rounding errors, he just found a way to keep them from piling up. Every float is positioned relative to its container, rather than the float before it. It’s a bit of a hack, and removes content from the flow, so I don’t recommned building your entire layout on isolated floats, but it can be very useful as a spot-check when rounding errors are really causing you a headache.

(Note that rounding errors can still stack up when you use a gradient background for testing. Gradient background grids are useful, but you should never trust them as a pixel-exact guide.)

Using John’s method, you can now isolate any grid element in susy, with the simple isolate() mixin:

.span {
  @include span-columns(6);
span 6
.isolate {
  @include span-columns(6);
  @include isolate(3);
span 6 isolate 3

When you put several of those together, you can see how they have been removed from the flow:

.first {
  @include span-columns(3);
  @include isolate(2);
.second {
  @include span-columns(4);
  @include isolate(9);
.third {
  @include span-columns(6);
  @include isolate(4);

The items can overlap, and stack in any order — almost as though they are positioned absolutely.

Isolation Grid

Isolation is most useful when you are repeating the same grid math again and again, such as image-galleries. To help with that use-case, we’ve added the isolate-grid() mixin. You just tell us how wide each item should be, and we’ll calculate the locations, applying them with nth-child selectors:

.gallery-item {
  @include isolate-grid(1);

Change the width, and we’ll update everything for you:

.gallery-item2 {
  @include isolate-grid(3);


Bleed has nothing to do with isolation, it just happened to appear in the same update. Bleed uses negative margins and equal-but-positive padding to let an element’s background “bleed” outside the area it would normally occupy.

Here’s an element bleeding 1-column outside our 9-column page layout:

.bleed-demo {
  @include bleed(1 of 9);

You’ll notice that the context syntax is a bit different here: (1 of 9) instead of (1,9). That’s the direction we’re heading with Susy 2.0, and it’s very helpful in this case, because there’s another argument we want to access easily. Use the second argument to list which sides should do the bleeding (defaults to “left right”). You can also pass arbitrary widths in the first argument:

.bleed-sides-demo {
  @include bleed(3 of 9, left);
  @include bleed(3em, top);
  @include bleed(6px, right bottom);
bleed all the sides!

This can be especially useful to bleed across $grid-padding. Simply bleed($grid-padding) and you’re there.

Happy coding!

Miriam Suzanne is a product manager, user-experience designer, writer, speaker, and open-source developer.

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