Absolute Horizontal And Vertical Centering In CSS

Absolute Horizontal And Vertical Centering In CSS

We’ve all seen margin: 0 auto; for horizontal centering, but margin: auto; has refused to work for vertical centering… until now! But actually (spoiler alert!) absolute centering only requires a declared (variable) height and these styles:

.Absolute-Center {
  margin: auto;
  position: absolute;
  top: 0; left: 0; bottom: 0; right: 0;
}

I’m not the pioneer of this method (yet I have dared to name it Absolute Centering), and it may even be a common technique, however, most vertical centering articles never mention it and I had never seen it until I dug through the comments section of a particular article.

There, Simon linked to this jsFiddle that blew every other method out of the water (the same method was also mentioned by Priit in the comments). Researching further, I had to use very specific keywords to find some other sources for this method.

Having never used this technique before, I put it to the test and discovered how incredible Absolute Centering really is.

Browser Compatibility:

Absolute Centering was tested and works flawlessly in the latest versions of Chrome, Firefox, Safari, Mobile Safari, and even IE8-10. One user reported that the content is not vertically centered in Windows Phone’s browser, but otherwise this technique works as expected.

If you find any additional features or issues, please leave a comment on CodePen.

Within Container

Place your content block inside of a position: relative container to perfectly center your content within the container!

.Absolute-Center {
  width: 50%;
  height: 50%;
  overflow: auto;
  margin: auto;
  position: absolute;
  top: 0; left: 0; bottom: 0; right: 0;
}

This box is absolutely centered, horizontally and vertically, within its container using
position: relative

Within Viewport

Set your content block to position: fixed and give it a z-index to keep it centered in the viewport.

  • Mobile Safari: The content block will be centered vertically in the whole document, not the viewport, if it is not within a position: relative container.
.Absolute-Center.is-Fixed {
  width: 50%;
  height: 50%;
  overflow: auto;
  margin: auto;
  position: fixed;
  top: 0; left: 0; bottom: 0; right: 0;
  z-index: 999;
}

See the Modal Demo page.

Responsive

Perhaps the best benefit of Absolute Centering is that percentage-based width/heights work perfectly! Even min-width/max-width and min-height/max-height styles behave as expected for responsive boxes.

Go ahead, add padding to the element; Absolute Centering doesn’t mind!

.Absolute-Center.is-Responsive {
  width: 60%; 
  height: 60%;
  min-width: 400px;
  max-width: 500px;
  padding: 40px;
  overflow: auto;
  margin: auto;
  position: absolute;
  top: 0; left: 0; bottom: 0; right: 0;
}

This box is absolutely centered, horizontally and vertically, even with percentage based widths & height, min-/max-, and padding!

Offsets

If you have a fixed header or need to add other offsets, simply add it in your content block’s styles like top: 70px;. As long as margin: auto; is declared, the content block will be vertically centered within the bounds you declare with top left bottom and right.

You can also stick your content block to the right or left while keeping it vertically centered, using right: 0; left: auto; to stick to the right or left: 0; right: auto; to stick to the left.

.Absolute-Center.is-Right {
  width: 50%;
  height: 50%;
  margin: auto;
  overflow: auto;
  position: absolute;
  top: 0; left: auto; bottom: 0; right: 20px;
  text-align: right;
}

This box is absolutely centered vertically within its container, but stuck to the right with right: 0; left: auto;

Overflow

Content taller than the block or container (viewport or a position: relative container) will overflow and may spill outside the content block and container or even be cut off. Simply adding overflow: auto will allow the content to scroll within the block as long as the content block itself isn’t taller than its container (perhaps by adding max-height: 100%; if you don’t have any padding on the content block itself).

.Absolute-Center.is-Overflow {
  width: 50%;
  height: 300px;
  max-height: 100%;
  margin: auto;
  overflow: auto;
  position: absolute;
  top: 0; left: 0; bottom: 0; right: 0;
}

This box is absolutely centered within its container, with content set to overflow.

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Images

Images work too! Apply the class/style to the image itself and set height: auto; like you would with a responsively-sized image to let it resize with the container.

Note that height: auto; works for images, but causes a regular content block to stretch to fill the container unless you use the variable height technique. It’s likely that browsers have to calculate the height for the rendered image, so margin: auto; ends up working as if you’d declared the height, in all tested browsers.

.Absolute-Center.is-Image {
  width: 50%;
  height: auto;
  margin: auto;
  position: absolute;
  top: 0; left: 0; bottom: 0; right: 0;
}

Variable Height

Absolute Centering does require a declared height, however the height can be percentage-based and controlled by max-height. This makes it ideal for responsive scenarios, just make sure you set an appropriate overflow.

One way around the declared height is adding display: table, centering the content block regardless of content length.

Caveats:

This will break cross-browser compatibility. You may want to consider the Table-Cell method in this case.

  • Firefox/IE8: Using display: table aligns the content block to the top, but is still centered horizontally.
  • IE9/10: Using display: table aligns the content block to the top left.
  • Mobile Safari: The content block is centered vertically, but becomes slightly off-center horizontally when using percentage based widths.
.Absolute-Center.is-Variable {
  display: table;
  width: 50%;
  overflow: auto;
  margin: auto;
  position: absolute;
  top: 0; left: 0; bottom: 0; right: 0;
}

This box is absolutely centered vertically within its container, regardless of content height.

Other Techniques

Absolute Centering works really well for many cases, but there are other methods that may fit more specific needs. The most commonly recommended methods are Negative Margins, Transforms, Table-Cell, and now Flexbox. These techniques are covered more in depth in other articles, so I’ll only go over the basics here.

Transforms

One of the simplest techniques with about the same benefits as Absolute Centering, but supports variable height. Give the content block transform: translate(-50%,-50%) with the required vendor prefixes along with top: 50%; left: 50%; to get it centered.

.is-Transformed { 
	width: 50%;
	margin: auto;
	position: absolute;
	top: 50%; left: 50%;
	-webkit-transform: translate(-50%,-50%);
    -ms-transform: translate(-50%,-50%);
        transform: translate(-50%,-50%);
}
      

Advantages:

  • Variable height content
  • Requires minimal code

Caveats:

  • Won’t work in IE8
  • Need vendor prefixes
  • Can interfere with other transform effects
  • Results in blurry rendering of edges and text in some cases

Futher Resources

Read more about Transform Centering in Chris Coyier’s article “Centering Percentage Width/Height Elements” on CSS-Tricks.

This box is absolutely centered vertically within its container using translate(-50%,-50%).

Table-Cell

This may be the best technique overall, simply because the height can vary with the content and browser support is great. The main disadvantage is the extra markup, requiring a total of three elements to get the final one centered.

Markup:

<div class="Pos-Container is-Table">
  <div class="Table-Cell">
    <div class="Center-Block">
    &lt!-- CONTENT -->
    </div>
  </div>
</div>
      

Styles:

.Pos-Container.is-Table { display: table; }
.is-Table .Table-Cell {
  display: table-cell;
  vertical-align: middle;
}
.is-Table .Center-Block {
  width: 50%;
  margin: 0 auto;
}
      

Advantages:

  • Variable height content
  • Content overflows appropriately
  • Works well cross-browser

Caveats:

  • Requires extra markup

Futher Resources

Read more about Table-Cell Centering in Roger Johansson’s article “Flexible height vertical centering with CSS, beyond IE7” on 456bereastreet.

This box is absolutely centered vertically within its display: table-cell parent, which is within a display: table container.

Flexbox

The future of layout in CSS, Flexbox is the latest CSS spec designed to solve common layout problems such as vertical centering. Smashing Magazine already has an article on Centering Elements with Flexbox that you should read for a more complete overview. Keep in mind that Flexbox is more than just a way to center, it can be used for columns and all sorts of crazy layout problems.

.Pos-Container.is-Flexbox {
  display: -webkit-box;
  display: -moz-box;
  display: -ms-flexbox;
  display: -webkit-flex;
  display: flex;
  -webkit-box-align: center;
     -moz-box-align: center;
     -ms-flex-align: center;
  -webkit-align-items: center;
          align-items: center;
  -webkit-box-pack: center;
     -moz-box-pack: center;
     -ms-flex-pack: center;
  -webkit-justify-content: center;
          justify-content: center;
}
      

Advantages:

  • Content can be any width or height, even overflows gracefully
  • Can be used for more advanced layout techniques.

Caveats:

Futher Resources

Read more about Flexbox Centering in David Storey’s article “Designing CSS Layouts With Flexbox Is As Easy As Pie” on Smashing Magazine.

This Flexbox box is absolutely centered vertically within its container.

Summary

Each technique has its advantages and disadvantages. Which one you choose mainly boils down to which browsers you support and what your existing structure looks like.

Absolute Centering works great as a simple drop-in solution with no-fuss. Anywhere you used Negative Margins before, use Absolute Centering instead. You won’t have to deal with pesky math for the margins or extra markup, and you’ll be able to size your boxes responsively.

If you need variable height content cross-browser, try out the Table-Cell or Flexbox techniques to see what works best for your site.

(vf)



Source Article from http://www.smashingmagazine.com/2013/08/10/absolute-horizontal-vertical-centering-css/