All language subtitles for 003 CSS Positioning_en

Now, so far we've seen a lot of different intermediate concepts already in this section.

Now I want to talk about something that is related to the positioning of elements on screen.

And there are four different types that we're going to go through Relative, Absolute Fixed and Static

positioning.

When developers don't understand positioning or in this case, when building developers don't understand

positioning, something like this might happen either on your building, which is terrible, or on your

website, which is also not great.

So we're going to understand this concept in order for this to not happen.

Now, if you're doing renovation work in your builders are doing this, then I'm not sure this video

is going to help, but it's definitely going to help us position our items in our websites a lot better.

As I mentioned, there are four different values for that property position.

It's static, relative, absolute and fixed.

And I want to show you how each of these values work and consider when you would need them.

So the first one is Static positioning, and this is actually the HTML default.

As soon as you insert any piece of HTML by default, they're going to have this particular positioning

applied to them.

And this basically means that each item flows as they would in our HTML.

Now, if you head over to this website appbrewery.github.io/css-positioning, then you

can see that I've created a demo website for you to interactively see what each of these different styles

of positioning would look like.

Now, if the font here is too small because I needed to get enough space in here to scroll, feel free

to go to view and then click on zoom in and press the plus button until it fits whichever size your

eyes require.

Once you're here, you can click on the different styles of positioning, and the first style is static

positioning.

We can set the position property to a value of static, but we also don't have to,

this is just applied by default.

In this case, this is just what default HTML does when you add another item here,

so, in this case, I've got a div here which I've colored green,

once this has been added, it just goes at the bottom of whatever previous element there is and you

can see this quite easily if you've installed the pesticide Chrome plugin.

Previously I showed you how to get hold of the pesticide chrome extension and now if we hold down our

control key, you can see we've got an "h2" here, and then we've got a "code" element here,

and then finally we've got a div element here.

So notice how that div just goes right at the end of whatever previous element there is.

And we can also inspect the code here to see this is where it is, and it simply just continues in the

default positioning.

This is what static does.

It's just what you've seen so far.

Now what's more interesting are the other three different types and one of the most common ones you're

going to come across that you're probably going to use is Relative positioning.

And this is where an item gets positioned relative to its default position.

Remember, previously in our static positioning, I told you that HTML just makes your items go one on top

of the other with almost no space in between unless there is some sort of default.

Well, relative positioning, basically takes that original position and you can apply some changes to

it.

So you can move it relative to where it should be.

So in this case, where the purple box is, is where it should be and where the blue boxes, it's been

shifted to be pushed from the left and from the top.

So that gets this new relative position.

Again, coming back to our website, if we select relative positioning, notice how these two other

parts of our code now is relevant.

We've got a push from the left and a push from the top.

Whereas originally this box was supposed to be somewhere here-ish.

I'm just going to draw a dashed line for where it was when we had the static positioning.

This is where it's supposed to be.

Instead, we've moved it 50px from the left using this line, and then we've moved it 50px

from the top using this line.

And this works because it is positioned relative to the original supposed location.

So now if we select this box, you can see it has position, relative left 50px, top 50px.

And this box, if we select it, you can see it has position static, which means that the left and

the top, it doesn't actually do anything because it's static position.

So it's just default position.

It doesn't matter if you add these properties, which you can, it just doesn't do anything.

That's the difference between relative and static positioning.

Relative positioning takes the static position and then you can move it relative to that location.

Now, remember, relative does not mean relative to anything else,

it's relative to its supposed location.

Some people get that confused and they think it's relative to something else on screen,

no. No.

We're going to remember this when you use relative positioning.

Now, the next type is Absolute positioning, and this makes the position relative to the nearest positioned

ancestor.

Now, this sentence is a little bit confusing, but remember, in the previous lesson we spoke about

the ancestors.

So for example, if I had a div here that is a purple box and inside that purple box I put in another

div, which is a blue box.

Well, in this case the blue box is a descendant and the purple box is an ancestor.

If this particular div has the position property set, for example, if we set this as relative and

we set the blue box to have a position as absolute, then this blue box is then going to be positioned

relative to its positioned ancestor.

And notice the wording here,

the nearest ancestor, it could have multiple ancestors with position relative, but it's the nearest

one that matters.

If it doesn't have a positioned ancestor, then the second rule becomes valid,

where it gets positioned relative to the top left corner of the web page, which is right here.

Now, if you go and select the absolute positioning, notice how this box is now wildly weird in terms

of its position,

and this is because it has no ancestor that has the position property set.

If we select our div right here, you can see this is where it is, and its ancestor is this div.

And then going further up we've also got this "main" element which is also another ancestor and then we've

got the body, and then the HTML.

So this is the flow of how we get to this descendant.

Now, because neither this div, nor this "main" nor the body, nor the HTML have the position property

set, well then in that case, this box is positioned relative to the top left of the web page.

And what we said is position absolute,

top: 50px;

left: 50px;

And that's exactly what it has done for us.

It's pushed it from the top by 50px and it's pushed it from the left by 50px,

and this is relative to the top left corner of the web page.

Remember that the first part of the absolute positioning rule is that if it had a positioned ancestor,

then it would be positioned relative to that ancestor.

So we can actually change our code here inside the inspector for let's say we're going to take this

box.

So make sure you've actually selected the right box that has the absolute positioning, as you can see

here.

And let's find its ancestor.

The first one I can see is this one.

So we're going to select it and then we're going to add a CSS rule.

So we're going to go inside the element.style, which is going to add an inline style to this element

we've selected, and I'm going to set its position to relative.

Now notice how as soon as I've done that, our box has moved, and now what it's done is it's moved so

that these rules that we've applied to this box, namely push it down from the top and push it down

from the left, is now relative to its nearest positioned ancestor, which is this div right here.

And if you look at this, you can see it has followed that rule.

It's pushed it 50px from the top of this div and 50px from the left of this div.

And it makes this true.

And that's because we've got that code here on the box.

The tricky thing about the absolute positioning is you have to make sure if you want it positioned relative

to another item, you have to set that ancestor to have position relative because otherwise it's going

to default to positioning relative to the top left of the web page.

Now another aspect of absolute positioning that's important to mention while we're here is the z-index (Zed),

as we would say in the UK, or if you're American, it would be the z-index (Zee).

Now what this does is it determines which elements go on top of which in the Z-axis.

If we think of our web page as a graph where we have the Y-axis going this way,

the X-axis going horizontally this way, then we can also have a Z-axis, which actually goes in the

third dimension, and that's the Z-axis.

This basically just determines which one goes on top of which.

If A has a higher z-index, let's set it to 100

and B had a lower z-index,

let's say it was 50, then this one is going to come out trumps and A is going to sit on top of B.

And you can see this already happening with our absolute positioned box.

You can see it's sitting on top of everything else.

If we wanted to not do that, say we wanted to make this box go behind everything, well then we can

set this property called z-index and we can make it even negative if we wanted to.

Everything on screen has a default z-index of zero.

But notice how even if I set the z-index of this box to zero, it still doesn't fit in with everything

else,

and that's because when you set something with absolute position, it actually takes the element out

of the original HTML flow and puts it on another layer.

This is why we can quite easily change it to a negative z-index to push it behind or use the default,

which will take it above, but we can't actually have it inside the flow anymore.

For that to happen, we need to go back to static position or relative position.

Now, the final type of positioning I want to talk about today is Fixed positioning.

And this is a position that is going to be relative to the top left corner of the browser window.

Remember how absolute position defaults to the top left of the web page, But in this case, when it's

fixed, it's going to be defaulted to the browser.

And what that means is that even if you scroll up and down on the web page, it's still going to be

located in the same location relative to the browser.

So this is where a demo comes in really handy.

Let's go into fixed positioning and notice it looks the same as our absolute position until you start

scrolling and notice how it's just staying right there with 50px are pushed down from the top and

from the left.

And it doesn't matter where you scroll to, it's always going to hover right there.

Whereas with absolute positioning, you can see it's relative to the web page and it moves with the

web page.

So have a think about this when you're using these different position styles in terms of what you want.

Notice how in all four different positional values, I've set it to have a top and a left, and this is

how we position things in addition to that "position property."

So you can also change this and set it to instead of left.

You can change that to right and it would just move it to the right instead and have 50px from

the right.

But in addition, you can also add extra margin.

So notice how position actually goes outside of margin in the box model.

So I can add an extra 50px of margin and it will push it even further

over here. The position is actually separate from the margin, which in turn is separate from the padding,

which in turn is separate from the width and the height.

But the really nice thing about position is notice how it's calculating these other values for you so

that you maintain these positional values of 50 from the top and 50 from the right.

And as I move it around, you can see how it's reacting to it,

it's just changing the left side automatically to keep it in that position.

If all of that seemed a little bit confusing, don't worry, we're going to solidify our knowledge by

practicing it and writing it in code in an exercise.

So go ahead and download the exercise from this lesson, CSS Positioning and extract it.

And then once you open it, go ahead and open the index.html and then preview it on the right hand side

right here.

You'll notice that it's an absolutely blank page because all we have in the HTML is a single div that

contains another div.

But by the end of this exercise, what we're aiming to do is to create a rectangle with a circle inside.

Before you start, I first want to show you how you can create a circle using CSS.

This is something that we haven't seen yet, so if I go ahead and target this ".red-circle", using the class

selector, I can give it a background-color of red so that we can actually see it on screen.

And I'm also going to give it a width and a height.

So it's going to be 200px across and 200px high.

And once I've done that, you can see I've now got a square on the screen.

So without a width and a height, of course it's not visible and this is stuff that you should already

know.

So there's nothing new here.

But if I go ahead and add a border-radius which will define the radii of the outer border.

Notice what happens here.

Let's go ahead and give it a 5px border-radius,

makes the corners a little bit rounded. So we can extend this,

let's try 50px and you can see it now

looks like an app icon almost, a little rounded square.

But I can also use percentages.

So if I set it to have a 50% border radius, then I create a perfect circle.

And this is how we create circles in CSS.

Now that you've got this red circle, it's only a matter of time before you get to the final outcome,

which is a circle positioned on top of a rectangle.

Now notice some things here,

we want the rectangle to be 300px tall and 500px wide, and we also want it to be positioned

not using any margins, but using the position properties to be pushed down 200 from the top, 200 from

the left.

In addition, we want this circle to be positioned relative to the rectangle and 250 from the left,

150 from the top.

This is going to test what you've learned and if you can't figure out how to do it, I recommend instead

of going forwards and looking at

the solution, go backwards in the video and revise what we learned about positioning and you will eventually

be able to get there.

I promise you it's not too difficult, but you do have to do a little bit of thinking.

Pause the video and try to complete this challenge.

All right.

So let's go through the solution.

But before we do, I want to make sure you really try to understand the lesson, because pushing through

with the code is not going to help you unless you actually understand what you're doing.

Coding is all about thinking.

It's not about memorizing things,

tt's not about knowing the answer because you're going to get a different situation in the future and

you need to make sure you know why things happen,

and that requires a little bit of struggle.

Let's go through the solution.

So I'm going to create this rectangle which has a class of ".blue-box", and I'm going to give it a background-color

of blue, and we see it show up because it contains a child element that has a height and width.

So the parent obviously then has to have a height and width, but that's not the height and width that

we want.

We want it to be 300px in height

and we want it to have 500px in width.

So now we have our rectangle and our circle correctly sized.

Now it's all about positioning.

Firstly, let's position this rectangle.

We want it 200px from the top, 200px from the left.

We can either do this using absolute positioning because it will be relative to the top left if we don't

set any of the other elements to have a position, or we can set it using relative positioning.

Because remember that the default location is also going to be at the top left corner.

I'm going to use relative positioning and you're going to see very quickly why.

But let's go ahead and set the position to relative and then let's set it to have a top of 200px

to push it down 200px here, and then let's give it a left of 200px so that it's pushed 200px

from the left.

And now we have this sort of image, which is already pretty close.

Now we just have to move the circle and this is where that relative positioning is going to come in

handy because we want to position this circle relative to the box.

Notice how all of these sizes I've given are relative to this blue box.

So 150px from the top, 250px from the left.

And this is easily achieved if we set the position to absolute and then we set the top to push down

by 150px and the left to push by 250px.

And now you can see we have exactly the same thing as our goal.

Now notice these numbers that I've given here 150px, 250px,

basically they are half, 250 is half of 500

and 150 is half of 300.

Essentially, I wanted the top left corner of this circle to be right in the middle of the rectangle.

Alternatively to setting these pixel values, you could have also set it to 50% from the top and 50%

from the left.

It would achieve exactly the same thing.

But notice how this doesn't place it in the middle of the rectangle, as some people would think, because

this is the point that we're defining the top left corner of this div now, even though the corners

are rounded, it doesn't mean that this div isn't a box, it's still a box.

It's the CSS box model.

All we've done is we've said the top left corner should be 50% of the width from the left of the rectangle

and 50% from the top of the rectangle.

So if you wanted this circle to be bang in the middle, you would actually have to specify different

values for the top and the left.

Now you could have actually solved this challenge in many different ways,

this didn't have to be relative and this didn't have to be absolute.

You could have, for example, set this position to be absolute because then it would make this blue

box relative to the top left corner because it doesn't have any other ancestors which have a position.

Alternatively, you could have set this to fixed because in this case we don't have any other content

on our website, so it doesn't actually scroll.

And so you won't see that movement relative to the browser.

As you can see, there's many ways of doing the same thing,

but the important thing is when your code gets more complex when there's more items in your HTML that

you understand what your CSS is doing and how to resolve any conflicts or when it's not doing what you

expect it to.

So

that you understand what code you're actually writing and how it's behaving.

Now that we know a little bit more about positioning, we can head over to the next lesson where I've

got a final project for this section where we're going to create the flag of Laos using everything we've

learned so far.

For all of that and more, I'll see you there.