By Guy Routledge

AtoZ CSS Quick Tip: Solving Common CSS Problems

By Guy Routledge
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This article is a part of our AtoZ CSS Series. You can find other entries to the series here.
You can view the full transcript and screencast for its corresponding video about the letter Q, the quotes property, here.

As a bonus bit of content in this article as a part of our AtoZ CSS Series, I’ve answered the most common questions I’ve received about CSS which I hope will be useful.



Q is for Questions about CSS

There is literally nothing else to say on the topic of CSS quotes, nor is there any other selector, property or value that starts with Q. So, in this week’s tips, I answer some common questions I get from my students, AtoZ supporters and fellow professionals.

How do you center things vertically in CSS?

I get this one a lot. And I get this one in addition to the more general question of how to horizontally center things in CSS which I addressed in an earlier tip all about floats.

On the topic of vertical centering, some people will tell you it’s really difficult. But these days it doesn’t require much CSS and can be done on any element – even in a responsive project when you don’t know how wide or tall the container or the element to be centered is.

Take the following HTML which marks up a simple .modal message box inside of a container:

<div class="modal"> 
  <h2>Message title</h2> 
  <p>Message text lorem ipsum dolor sit amet</p> 

To absolutely center the .modal element we can combine absolute positioning with translate.

Step one is to put the top left corner of the box right in the center of the parent container – which we can do by offsetting its top and left edges by 50% of the height and 50% of the width of the parent container:

.container {position: relative; width: 100vw; height: 100vh;} 
.modal {position: absolute; top: 50%; left: 50%;}

Step two is to bring the element back into the absolute center of the container. We need to move it back by half of its width and up by half of its height.

If we know the dimensions of the .modal we can achieve this with some negative margin and divide the width or height by 2 to get the required value. But if the .modal is likely to change size (due to being sized with percentages for example) this won’t work.

Instead, using a translate transformation, we can move the element by a percentage of its existing size.

.modal {position: absolute; top: 50%; left: 50%;}
/* back by half its width, up by half its height */
transform: translate(-50%, -50%);

And there you have it, the element is perfectly centered even with a variable size.

How do you deal with vendor prefixes in CSS?

You may have noticed in the first tip about vertical centering that I used a transform without adding the vendor prefixes. This is for two reasons. Firstly, it makes tutorial code easier to read and type and secondly for one little secret: I don’t write any vendor prefixes anymore.

I still occasionally find myself at the excellent to check on browser support for various properties and features but these days I don’t write any prefixes in my code.

This is not because I don’t care about users of browsers other than the one I develop in. And it’s not because I’m lazy and a bad developer. I don’t write vendor prefixes because I have an automated task that adds them for me, so I never have to think about them again.

I’d highly recommend using a pre-processor to write your CSS (I use Sass but have also used all the others to try them out) and I’d recommend adding Autoprefixer to your process too. Autoprefixer is a plugin for PostCSS which automatically adds the necessary prefixes to your compiled CSS based on the data from

There are plugins available for all the popular task automators and I can’t recommend it highly enough!

My CSS isn’t working. Can you help?

The short answer is, probably. But it’s always really hard to debug someone’s code remotely or based on a description of the problem. Instead, let me outline my process for debugging wonky CSS:

  • Check the relevant files are saved
  • Check the syntax highlighting in your editor and look for any inconsistencies
  • Check for missing quotes, brackets or semi-colons
  • Ensure the files I’m editing are what I’m looking at in the browser
  • Ensure any paths are correct (for CSS files, images or anything else). You can check to see that all your external files have been loaded correctly in the Network, Sources or Console tabs in your developer tools
  • Inspect element and ensure that all class names have been spelled correctly
  • Inspect element and ensure that all CSS properties have been spelled correctly (in Chrome, any invalid properties or values will be marked with an orange alert icon in the elements view)
  • Inspect element and play around with values to see what changes
  • It’s likely that you’ll have caught the issue by now but if not, some deeper digging is needed

This may be a good point to ask for help either online or in person. If you do ask people for help, make sure you can send them a link to a Codepen or JSFiddle of your problem so they can see what you’re struggling with.

Grunt or Gulp?

It took me a while to get on board with Grunt but eventually I did. To start with I didn’t really get what it was for but when I realized I could use it to launch a local server, compile my Sass, compress my JavaScript and alert me to any syntax errors while I type, I was convinced. It took me a while to get used to but I was happy.

When I heard about Gulp (which is a tool that does basically the same stuff but in a different way) I took the stance of “if it isn’t broken, don’t fix it.”

But I was wrong.

I recently worked on a client project as part of a team and they were already using Gulp so I used it too and wow, it’s fast! Compiling Sass used to take many seconds with Grunt but with Gulp we’re talking milliseconds.

I’ve totally converted and until something better comes along, I’ll be sticking with Gulp.

So I hope you found those questions and answers interesting or useful. If you have any further questions, please don’t hesitate to get in touch and let me know how I can help you.

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