The CSS Grid layout system is probably my favorite tool for design these days. With Grid, you can do so many amazing tricks that would have been nearly impossible a decade ago. I discussed some of the basics of Grid in an earlier post, but let's dig a little deeper today.
What is Grid?
CSS Grid is a layout system for designing pages with content that needs to be arranged in two dimensions. This sets it apart from the Flex layout system, which is intended for arranging elements along a single dimensional axis. Grid works like the traditional layout grid for which it's named, establishing rows and columns and placing elements into cells or areas at the intersections.
Unlike traditional HTML tables, which also allow for arranging elements in two dimensions, CSS Grid allows for more sophisticated relationships. Elements can overlap each other and layer intelligently, for example. And a Grid layout can be dynamic, adjusting itself based on varying numbers of elements or even the size of the viewport.
Setting Things Up
Any Grid layout first needs a grid container, an element with
display: grid. This establishes that every direct child within the container will be a grid item. Without any extra CSS, the browser uses a few important defaults to render this grid:
- The grid has a single column that is as wide as the grid container.
- Each grid item generates its own row, which display one after the next.
- Each column starts and ends at invisible, vertical grid lines. Similarly, each row starts and ends at invisible, horizontal grid lines. These lines are numbered, starting at 1, so our single column starts at line 1 and ends at line 2. (We can reference these lines in CSS, and we will in a bit.)
Assuming all of the grid items are normal block elements, the result won't look any different than normal flow layout. So how do we shake this up?
grid-template-columns define tracks for our grid.
Grid tracks are the spaces between the invisible numbered lines. By default, the browser creates one vertical track (our single column) and as many horizontal tracks as it needs to fit all child elements. But we can deviate from that default by setting the
The simplest way to do this is to set specific lengths for the width of each column or the height of each row. That would look something like this:
grid-template-columns: 100px 100px 100px;
grid-template-rows: 100px 100px 100px;
This creates a grid with three columns, each 100 pixels wide, and three rows, each 100 pixels tall. Where two tracks intersect, we get a grid cell, so this grid would have nine cells, each 100 pixels by 100 pixels.
Whatever grid items we have in our container will be placed into these cells one by one, filling a row, then moving to the next. If there are fewer than nine grid items, the rest of the grid is blank. Any completely empty rows collapse.
But what if there's more than nine grid items? In such a case, the browser has to create new rows, and to do so, it relies on the implicit grid. This means that it creates a new row, but without a set size, that row is automatically sized based on the content of the grid items in it. These extra rows will probably not feature our ideal 100px-by-100px cells.
To avoid this, we can tell the browser what size to make the new rows in the implicit grid using the
grid-auto-rows property. In fact,
lets us simplify our grid above, if we don't always know that we'll have exactly nine grid items.
grid-template-columns: 100px 100px 100px;
Of course, setting exact measurements for our tracks will get tedious very fast, if we have content of many different sizes. We're better off letting the browser do the work for us, and that's where flexible sizes come in.
CSS Grid introduces a new length unit, the
fractional unit or
fr. If a track is
1fr in size, that means it will take up one full share of the available space, after accounting for anything with an absolute size, like
100px. If you have multiple tracks with
sizing, the browser adds up all of the
fr units and divides the available space proportionally. So, if you have the following grid...
grid-template-columns: 1fr 1fr 2fr;
...it would render with any item in the third column taking up half the total width of the grid container, and the items in the first two columns getting a quarter of the width each. If you had
grid-template-columns: 100px 1fr 1fr 2fr
instead, then the first column would always be 100px, and any remaining width would be divided up as before.
To simplify larger and more sophisticated layouts, CSS Grid introduces a few functions you can use within your
grid-template-* properties. The most important when you're starting out is
repeat(). This function takes two arguments: a number of times to repeat, and the actual value to be repeated. So,
repeat(3, 1fr) is the equivalent of
1fr 1fr 1fr.
The value to be repeated can be more complex, however. For example,
repeat(3, 50px 1fr) is the equivalent of
50px 1fr 50px 1fr 50px 1fr. No, I don't know why you would use that particular construction, but you can see how you could quickly build up more complicated layouts using
More to Come
We've only scratched the surface of CSS Grid. It's such a powerful tool, that I'll be following up on this in the next few posts. Until then, mess around with Grid and see what you come up with!