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Narrow and wide spread column math

Understanding ‘Spread’ in Susy3

Susy 3.0 will be released in the next week, if all goes well, and there’s a lot to write about it. I wanted to start with a detailed overview of one core concept: spread.

Spread isn’t new to Susy3, or even to Susy generally, but its full power is usually hidden behind other settings (like gutter-position in Susy2), or opinionated assumptions about your grid. We didn’t invent the idea behind spread – every grid system has to make these decisions – but we haven’t seen anyone else talking about it explicitly.

In Susy3 we’ve tried to move in the other direction – naming spread, and making it central to the API – giving you full control over the math.

Container-spread describes how a grid-parent (or container) handles available gutters. Most grids only put gutters between the columns. That means there will be one less gutter than there are columns. We call that a narrow container-spread, and make it the default.

Some grids use “split” gutters, with half of a gutter on either side of a column – forming full-gutters between columns, and an extra half at the edges. Mathematically, that means we have an equal number of gutters and columns. We call that a wide spread.

Occasionally, a grid will have full gutters on both sides, meaning there is one more gutter than columns. We call that a wider spread.

Spread describes the same concept as it relates to internal grid-spanning elements. In most systems, including the new CSS Grid module, all spans are narrow – meaning they only span intermediate gutters.

Occasionally it’s useful to span as many gutters as columns – a wide spread – if you have split-padding gutters, for example, or if you want elements to touch at certain places, or if you are pushing and pulling elements in the grid.

It’s rare that you need to span a wider spread, but we’ll let you decide if it’s useful.

In Susy3 there is no single grid “container” element that receives special treatment. Instead, container spans are described in the same syntax as any other span – and any element containing other grid-aligned elements is a container.

Fluid-span calculations require understanding both the container width and span-width. The Sass math looks like this:

$fluid-width: percentage($span-width / $container-width);

For that reason, it’s important to be explicit with Susy about the spread of both containers and spans, when you are building fluid grids. In the Susy3 syntax, that looks like:

$width: span(3 wide of 6 narrow);

If it comes before of, it describes the span. If it comes after of, it describes the container. In most cases, there will be a sensible default for both values, which you can set in the global settings:

// Both default to "narrow"...
$susy: (
  'spread': 'narrow',
  'container-spread': 'narrow',

Commonly, all spans have a narrow spread. In fact, the CSS Grid module doesn’t provide any way to span across extra gutters. You would have to achieve a wide or wider span using negative grid-gap-sized margins.

There are times when you simply want to span across a gutter, for the sake of style. But there are other common reasons to span extra gutters. Let’s look at a few.

Pushing, Pulling, & Padding Elements

It’s sometimes necessary to “push” and “pull” elements out of their usual flow position, or add grid-aligned padding. You can do that by using the span functions on the margin or padding of an element. Push with positive left margins, pull with negative right margins, and pad either side with the padding property.

In all those cases, you’ll probably need a wide span in order to align your content with the proper column:

Split Gutters

Some grid systems use “split” gutters, with half a gutter on either side of an element. That will add an extra gutter to your total grid width, giving your common container a wide spread. If you are using split gutters, you likely want to set container-spread: wide in your global settings.

Here’s a wide container, with narrow spans and split gutters:

If you move the gutters inside, using the padding property, both spread and container-spread may need to be wide. I say “may” because it also depends on your border-box-sizing. That’s a whole new article, and honestly: padding gutters make the math much simpler. If you use padding gutters, there’s a good chance you don’t need Susy.

More about that in my next post. Until then: Happy coding!

Keep an eye out for the Susy3 release, coming soon! Follow us on Twitter, or contact us online. We’re excited to hear from you!

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