Reverse order of columns in CSS Grid Layout

Question

I was hoping to use CSS Grid to reverse the apparent order of two side-by-side divs, where one of the divs grows arbitrarily (I don't want to use floats).

I've created a plunkr here: http://plnkr.co/edit/6WZBnHbwhD7Sjx2ovCO7?p=preview

#container {    grid-template-columns: 240px 1fr;    display: grid;  }    .a {    background: yellow;  }    .b {    background: blue;    color: white;  }    #container>.a {    grid-column: 1;  }    #container>.b {    grid-column: 2;  }    #container.reverse>.a {    grid-column: 2;  }    #container.reverse>.b {    grid-column: 1;  }

<div id="container" class="reverse" style="width: 800px;">    <div class="a">A</div>    <div class="b">B</div>  </div>

The crux of it is that when I have the .reverse class applied (so that you should see B | A), B is offset to a new line so it looks more like:

          | A B 

If I invert the document ordering of .a with .b, this goes back to normal (but of course, if I drop the .reverse class, I get the same problem).

Why is this, and how can I address?

Answer 1

As the Grid auto-placement algorithm lays out items in the container, it uses next available empty cells (source).

In your source code the A element comes before the B element:

<div id="container" class="reverse" style="width: 800px;">    <div class="a">A</div>    <div class="b">B</div> </div> 

Therefore, the grid container first places A, then uses the next available space to place B.

By default, the auto-placement algorithm looks linearly through the grid without backtracking; if it has to skip some empty spaces to place a larger item, it will not return to fill those spaces. To change this behavior, specify the dense keyword in grid-auto-flow.

^{http://www.w3.org/TR/css3-grid-layout/#common-uses-auto-placement}

---

grid-auto-flow: dense

One solution to this problem (as you have noted) is to override the default grid-auto-flow: row with grid-auto-flow: dense.

With grid-auto-flow: dense, the Grid auto-placement algorithm will look to back-fill unoccupied cells with items that fit.

#container {   display: grid;   grid-template-columns: 240px 1fr;   grid-auto-flow: dense; /* NEW */ } 

7.7. Automatic Placement: the grid-auto-flow property

Grid items that aren’t explicitly placed are automatically placed into an unoccupied space in the grid container by the auto-placement algorithm.

grid-auto-flow controls how the auto-placement algorithm works, specifying exactly how auto-placed items get flowed into the grid.

dense

If specified, the auto-placement algorithm uses a “dense” packing algorithm, which attempts to fill in holes earlier in the grid if smaller items come up later. This may cause items to appear out-of-order, when doing so would fill in holes left by larger items.

#container {    display: grid;    grid-template-columns: 240px 1fr;    grid-auto-flow: dense; /* NEW */  }    .a {    background: yellow;  }    .b {    background: blue;    color: white;  }    #container>.a {    grid-column: 1;  }    #container>.b {    grid-column: 2;  }    #container.reverse>.a {    grid-column: 2;  }    #container.reverse>.b {    grid-row: 1;    grid-column: 1;  }

<div id="container" class="reverse" style="width: 800px;">    <div class="a">A</div>    <div class="b">B</div>  </div>

---

grid-row: 1

Another solution would be to simply define the row for the second item.

#container>.b {   grid-column: 2;   grid-row: 1; /* NEW */ } 

#container {    display: grid;    grid-template-columns: 240px 1fr;  }    .a {    background: yellow;  }    .b {    background: blue;    color: white;  }    #container>.a {    grid-column: 1;  }    #container>.b {    grid-column: 2;    grid-row: 1; /* NEW */  }    #container.reverse>.a {    grid-column: 2;  }    #container.reverse>.b {    grid-row: 1;    grid-column: 1;  }

<div id="container" class="reverse" style="width: 800px;">    <div class="a">A</div>    <div class="b">B</div>  </div>

Answer 2

I'm not sure how to reverse more grid items. But if you have 2 grid items in your grid, you can simply position 2nd grid item using below code.

#container > .b {     grid-column-start: 1;     grid-row-start: 1; }