CSS Layout: Flexbox

Learning Goals

  • Explain what flexbox is and why its an important tool for creating layouts
  • Explain the difference between a parent and child element, be able to identify immediate children
  • Apply Flexbox to containers in order to achieve a desired layout


Read through Intro to Layout Pre-Work document and all links provided and complete exercises provided in it. Be prepared to demonstrate your understanding of the concepts in that document when you come to this class.


  • flexbox - a layout method for laying out items in rows or columns. Items flex to fill additional space and shrink to fit into smaller spaces
  • display - a css property that sets whether an element is treated as a block or inline element and the layout used for its children, such as grid or flex
  • flex parent or flex container - Any HTML element that has been given the display: flex declaration
  • flex child or flex item - Any immediate descendants of a flex parent
  • main axis – the primary axis along which flex items are laid out. It can be horizontal or vertical, and is defined by the direction set by the flex-direction property.

Warm Up

  • With a partner, fork this codepen
  • Explore the CSS that’s already present. Without googling, what do you think :nth-child means?
  • In your CSS, add the property of “display” with a value of “flex” to the .wrapper selector. What happened? Which elements visually changed?

What is Flexbox?

Flexbox is a part of CSS that provides an efficient way to lay out, align and distribute space among items in a container. Before flexbox became popular, it was a real challenge to center elements. We would use something called float, which could behave unpredictably at times.

Parents and Children

As we start working with flexbox, a very important distinction should be pointed out. We need to be careful about the CSS rules we apply to a parent element vs. those to a child element. A parent element wraps other elements, a child is nested inside the parent.

Let’s look an some HTML to make sure we are all on the same page. Which element is the parent and which are its children?


The Answer

In the code above, the section is the parent element, the <h1> and the 3 articles are all children elements because they are directly nested inside of that section. Proper indentation is really helpful here!

What about in this block of HTML?

    <h2>Title of Article 1</h2>
    <h2>Title of Article 2</h2>
    <h2>Title of Article 3</h2>

The Answer

In the code above, we now have these h2 elements nested inside of each article. It’s important to know that the h2 is not an immediate child of the section. It is technically a grandchild, and a child of article. The idea of immediate child is really important to understand as we work with Flexbox.

When we use Flexbox, we will make the parent elements flex containers and the children elements flex items.

graphic of parent/container graphic of child/item
(Graphics from CSS Tricks)

Try It 1

  • Go back to your codepen from the warm up
  • Experiment adding the justify-content property to your .wrapper. Add the following values (one at a time), and note what changes:
    • center
    • space-around
    • space-between
    • space-evenly
    • flex-end

Justify Content

justify-content allows us to define the alignment of items (flex children) along the main axis, and is incredibly useful for centering elements.

  • flex-start (default): items are packed toward the start line
  • flex-end: items are packed toward to end line
  • center: items are centered along the line
  • space-between: items are evenly distributed in the line; first item is on the start line, last item on the end line
  • space-around: items are evenly distributed in the line with equal space around them
  • space-evenly: items are distributed so that the spacing between any two adjacent alignment subjects, before the first alignment subject, and after the last alignment subject is the same

Here is a great example of how you can use justify-content to move your items:

See the Pen Flexbox & justify-content by CSS-Tricks (@css-tricks) on CodePen.

The above Codepen is an example from CSS Tricks


Most flexbox-related properties have default values. We don’t see them in our CSS, but can know that they are being applied! These properties can always be changed by us. You’ll see some default values indicated below.

Try It 2

  • Go back to your codepen from the warm up
  • Now add flex-direction: column; to your .wrapper
  • What happened? How does changing the values for the justify-content property affect the boxes?

Flex Direction

Another CSS property with flexbox is flex-direction. This property takes one of four values:

  • row (default): left-to-right
  • row-reverse: opposite of row (right-to-left)
  • column: same as row but top to bottom
  • column-reverse: same as column but bottom to top

The flex-direction property defines the main axis

flexbox parent axis

Try It 3

  • Go back to your codepen from the warm up
  • Remove the justify-content and flex-direction properties.
  • Now, add in an align-items property and experiment with the following values:
    • stretch
    • center
    • baseline
    • flex-start
    • flex-end
  • Then, add flex-direction: column; to your .wrapper. What changes?

Align Items

Just like we can control how our content sits on the main axis with justify-content, we have a tool to control how our content sits on the cross-axis.

  • stretch (default): stretch to fill the container (still respect min-width/max-width)
  • flex-start: cross-start margin edge of the items is placed on the cross-start line
  • flex-end: cross-end margin edge of the items is placed on the cross-end line
  • center: items are centered in the cross-axis
  • baseline: items are aligned such as their baselines align

flex align values


These properties will get you far enough for now, but they’re just scratching the surface at what flex can do! If you want more, check out this extensive guide from CSS tricks.

Tips and Tricks (write these in your notes!)

When you are about to use flexbox, ask yourself the following questions:

  • What elements do I want to move?
  • What is the parent element of those elements? (this is where the flex properties should live!)

If flex isn’t working the way you think it should, check the following things:

  • Did I remember to include display: flex;? Without that line of code, the other flex properties won’t work!
  • Am I sure I’m adding the flex properties to the correct element? Check the parent-child relationship in the HTML file to be sure that you are adding those properties to the direct parent.
  • Is the parent element big enough? Add a border to the parent element. If it is the same width and/or height as the children, you won’t be able to move those children as expected.

Using Flexbox on Nested Elements

Try It 4

Recreating a Comp

We will now continue working on the comp from the CSS Fundamentals lesson. You will have one hour to work on iteration 2 of this activity.

Additional Resources

Lesson Search Results

Showing top 10 results