CSS can also be used to layout the page differently. Without this, you couldn't have two boxes next to each other, like this:

<style>
  .ex-box {
    border: 3px solid #aaa;
    background-color: #eee;
    height: 200px;
    width: 200px;
    display: flex;
    align-items: center;
    justify-content: center;
    float: left;
    margin-right: 10px;
    border-radius: 5px;
    font-size: 30px;
  }
  .ex-box:last-of-type {
    clear: right;
  }
</style>
<div class="ex-box">Box 1</div>
<div class="ex-box">Box 2</div>

Those are just two divs with some text inside. Without CSS, we wouldn't be able to control the width, height, the fact that they're side-by-side instead of on different lines, the space between them, or the vertical and horizontal centering of the text. We're getting into the more layout-oriented CSS.

The Box Model

We're going to talk about what is call the box model of CSS. This is one of the most confusing thing for people new to CSS to grasp at front, so it's worth investing time into understanding. It's important.

Display

Every tag in CSS has a display property associated with it by default. In fact, CSS has a lot of hidden defaults, just like by-default all text's color is black. With display, it varies by what type of tag we're talking about. divs are display: block; by default while spans are display: inline; and this makes sense given their functions. However, being that we have access to CSS, we can manipulate a span to act like a div and vice-versa (though usually you'd just use the appropriate tag.) We'll list out a few of the options here of what display can be.

• inline – Like it sounds, it makes whatever the tag is behave like text. If you I want to style some text inline, this is how to do. The key here is the browser will determine all the height, width, padding, margins, etc. for you and will not let you change it. This is a common pitfall for those learning. If you have something and you're trying to set the width or height and it's not respecting it, it's probably the wrong display type.
• block – divs and ps by default are display: block;. This give you control over the height, width, padding, margins, etc. of something. By default, something that is block takes the whole line to itself.
• inline-block – A hybrid of the previous two. This will make browser try to place the tag inline, but will still allow you to control the height, width, padding, and margins. Like this box:
  This wouldn't be possible with either of the previous.
• flex and inline-flex – Similar to block in that it affects the tags around it like block does, however it gains some new super power on how its interior tags are layed out. There's a section below where we'll talk about flex.
• grid and inline-grid – More advance display mode that allow you more power to layout tags inside of them. CSS-Tricks and Frontend Masters both have useful tutorials on these and they are definitely worth your time.
• table – Make something act like a table. In general, use the <table></table> tag instead of using CSS to make things act like tables.

Height, Width, Padding, Border, and Margin

Again, these properties cannot be manipulated if something is display: inline. Be careful of that.

Something is a block or block-like has several measurements that add up to its whole.

I'm using several elements here to concretely demonstrate how the box model works, but assume it was all one div tag. The css would look like:

.example {
  border: 3px solid red;
  padding: 5px;
  margin: 25px;
  background-color: white;
}

The background-color of the parent of the container is blue. The 2px dashed green border is added by me to show padding. So let's pick this apart, starting from the outside and working in.

• margin – This is the space outside of the element between it and other elements. It is outside of the border. If you give something a background-color, it will not color in the margin space. This is used to space elements out from other elements.
• border – Next is the border. If your element has a border, it comes next (not everything has or needs a border.)
• padding – Inside the border is the padding. This is the spacing inside the element. If you give something a background-color, you will color the padding space. In our diagram above, you can see the space between the red, solid border and the green, dashed border. This is the padding of the element.

Right now, the above element doesn't have a set height or width, which means it will take its height from what ever inside of it and it will try to take 100% of the width it can. We can modify both of these. However, if I say width: 200px, what is 200px wide? Unfortunately, the answer is it depends. It depends on what the value of the box-sizing property. By default, it does things the old way of writing code which if I say width: 200px I am not including the border or the padding. This is annoying because if I'm trying to fit things together well, it's much easier to include border and padding. Remember how I told you to never use the wild card selector before? This is the one exception where I permiss you to:

* {
  box-sizing: border-box;
}

This will make everything use the border-box sizing instead of the default one (which is called content-box but you'll never have to know that.) This is the first thing I put in every project I start. You'll need it once in one file. This will make everything by-default be border-box and thus be easier to work with. This used to be controversial to use but here is Paul Irish (really smart guy who works on Google Chrome) saying it's okay.

Laying Out Tags

There are a few ways to accomplish layouts. We'll briefly discuss two: floats and flex. There is also grid, but it's still new which means a significant of people's computers don't support it and the best practices for it are still being ironed out. In addition, you don't need it right away.

We're going to be using these boxes a lot over the next examples. Here's the CSS if you want to play with them:

<style>
  .box-1 {
    border: 1px solid black;
    color: white;
    background-color: blue;
    height: 150px;
    width: 300px;
  }
  .box-2 {
    border: 1px solid black;
    color: white;
    background-color: red;
    height: 100px;
    width: 300px;
  }
  .box-3 {
    border: 1px solid black;
    color: white;
    background-color: green;
    height: 200px;
    width: 100px;
  }
</style>
<div class="box-1">1</div>
<div class="box-2">2</div>
<div class="box-3">3</div>

Floats

The old, bullet-proof of laying things is using a property called float. The idea behind float is you'll an element to push itself as far left or right as possible, and once it's out of space, go to the next line. I'll put an example on the line below. Try resizing your browser horizontally and see the boxes re-arrange themselves.

<style>
  .floated div {
    float: left;
  }
</style>
<div class="floated">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

You'll see the boxes will wrap themselves once they run out of room and box 3 wraps as you would expect. However, once you wrap both boxes 2 and 3, you'll see that box 3 won't go all the way up next to 1; it stays at the same vertical position as 2. Since box 2 is higher in the HTML, box 3 cannot go higher on the page due to the way that CSS works. This is just one limitation of floats. They have peculiar behavior that's tough to understand. Let's move on and talk about flex which makes it much easier to handle.

Flex

display: flex; is a display mode for CSS. It's to note that when you stick display: float, it allows you to to change the layout inside the tag. It allows you to change the layout of its children. Externally, it acts just like block. Likewise there is a inline-flex which acts just like display: inline-block externally.

Flex allows for a lot of interesting patterns but we're going to scratch the surface today. Take Jen Kramer's course or read the CSS Tricks article to learn more. We're going to explore same case today. Flex lets you tell CSS how to lay out the items inside a tag. We can tell the them to be left aligned, bottom aligned, center aligned, whatever you want. You can even throw them into columns. I think this is best taught by example so let's just throw a bunch on the page. All of them will have the following CSS:

<style>
  .flex-container {
    display: flex;
    width: 100%;
    border: 1px solid black;
  }
</style>
<div class="flex-container">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

And we'll just be changing three properties: flex-direction, justify-content, and align-items. Nothing special will go on the boxes, just the style to make the colored boxes. So let's throw a bunch examples up.

No changes made, just the above CSS and HTML.

Looks similar to the floats, but notice if you make the page more narrow, the boxes will squish instead of wrapping.

<style>
  .reverse {
    flex-direction: row-reverse;
  }
</style>
<div class="flex-container reverse">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

It's backwards! Easy as pie to do it with flex. We can even make it a column!

<style>
  .column {
    flex-direction: column;
  }
</style>
<div class="flex-container column">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

Okay, so now we've done columns, (also, column-reverse works as you would expect) we're going to try affecting how the items are justified.

<style>
  .jc-right {
    justify-content: flex-end;
  }
</style>
<div class="flex-container jc-right">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

This is basically right-justified. Notice this is different from the reversed one about because the items stayed in the same order. By default, the justify-content is flex-start which is like left-justified.

<style>
  .jc-center {
    justify-content: center;
  }
</style>
<div class="flex-container jc-center">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

And here we see centered boxes. Let's explore the last two which aim to evenly space the boxes out in the space provided.

<style>
  .jc-sb {
    justify-content: space-between;
  }
</style>
<div class="flex-container jc-sb">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

This one puts the first on the left most and the last on the right most. It then aims to space out the items in the middle equally. Very useful for laying out columns on your web page. The last two are space-around and space-evenly. I'm just showing you space-around but space-evenly is very similar. Feel free to read more into it if you're interested.

<style>
  .jc-sa {
    justify-content: space-around;
  }
</style>
<div class="flex-container jc-sa">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

Notice the space between the items and the edges (as compared to before.)

So now we've shown you the justify-content property, let's examine align-items. justify-content worries about horizontal justification and align-items worries about vertical alignment. Let's take a look at a few examples.

<style>
  .ai-fe {
    align-items: flex-end;
  }
</style>
<div class="flex-container ai-fe">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

Notice how all the items are now pushed to the bottom of the element, the "end" of it (the opposite is, you guessed it flex-start.) This isn't always useful but I find myself constantly using the next one for centering items.

<style>
  .ai-center {
    align-items: center;
  }
</style>
<div class="flex-container ai-center">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

Vertically centering something previous to flex was a nightmare. Seriously, Google "vertically center CSS" and see the decades of anguish on StackOverflow. Luckily for you we now have flex and it makes vertically centering something as easy as align-items: center in a display: flex tag. Count your lucky stars!!

<style>
  .ai-stretch {
    align-items: stretch;
    height: 200px;
  }

  /* remove the height from the three boxes */
  .no-height {
    height: inherit;
  }
</style>
<div class="flex-container ai-stretch">
  <div class="box-1 no-height">1</div>
  <div class="box-2 no-height">2</div>
  <div class="box-3 no-height">3</div>
</div>

For this one I did have to remove the heights from the boxes or it overrules the stretch. Stretch makes the interior tags stretch to fit whatever container they're put in (unless they're limited by a height already.)

So now we've gone through the basics of flex. Obviously you can combine these to achieve various effects. We're going to re-use the CSS classes from above (if you messed with them, just refresh the page.)

<div class="flex-container ai-center reverse jc-sa">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

Or this:

<div class="flex-container ai-fe column">
  <div class="box-1">1</div>
  <div class="box-2">2</div>
  <div class="box-3">3</div>
</div>

Further Flex

There's a lot more power with flex you can achieve. You can make multiple rows using flex-wrap. There are also a slew of properties that the children elements can have (everything we have done so far goes on the parent class) that you can affect things like order using order and you can individually override the align-items using align-self. Cool stuff. Definitely dig into it further.