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is that they too can be mobile responsive.
6,186.82
2.4
They too can wrap around other lines if they ever need to.
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3.81
So, for example, let me pull up columns one.html.
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2.83
Here, for example, I have a row.
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2.27
And let's take a look at what's going on in here.
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2.05
Recall that every row in Bootstrap is divided up into 12-column units.
6,202.85
5.04
But Bootstrap, in addition to letting me specify how many units a column
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3.51
should take up, also lets me specify how many units that column
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3.45
should take up depending on the size of the screen.
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3.25
So if I'm on a large screen, as indicated by LG,
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3.95
this is saying that on a large screen, this div
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2.97
should take up 3 units of space.
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2.34
And this div should also take up 3 units of space.
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2.42
And for each of these four divs, on a large screen,
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2.98
each will take up 3 of the total 12 units of space.
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3.66
So they'll all show up on one row.
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2.91
What happens on a small screen, though?
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2.4
Well, here col sm, for column on a small screen,
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3.72
I've said on a small screen each column should only
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2.49
take up 6 units of space, 6, or half, of the total 12 that I have in the row.
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5.7
And so I use up 6 here, 6 here for a total
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2.16
of 12 in one row, which means the next two, also a size 6,
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4.29
need to go on to a second row.
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2.13
And Bootstrap is smart enough to do this math for me
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2.55
and figure out how exactly these elements should ultimately be laid out.
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4.44
So now if I open up columns 1.html and see what's there, on a large screen,
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8.21
I see four columns, all in the same row.
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2.91
But as I shrink down to a smaller screen,
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1.92
eventually we'll see that things change.
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3.15
I now see the third and fourth sections move down onto the second row,
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4.14
because on a smaller screen now, when the window is smaller,
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3.9
now I only have the ability to show two elements in any particular row.
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3.91
So I get to on the first row and then two on the row underneath that.
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5.14
So all in all, there are a lot of different ways
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2.32
now that we can use CSS in order to make sure our pages are mobile responsive.
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4.07
We can use Bootstrap column model to make
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2.25
sure the columns move around whenever a size of the window shrinks or grows.
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4.35
We can also use things like flexbox and the grid model,
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2.49
writing our own CSS to make sure that our page is responsive depending
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4.29
on the size of the screen that the user happens to be using in order
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3.3
to visit our website page.
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1.69
So these are some of the very powerful features that we get using just CSS.
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5.06
But one thing you might imagine is that as we begin to write more and more CSS,
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3.84
there's going to be more and more repetition, things that appear again
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3.81
and again and again.
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1.55
And we've already seen some ways that we can minimize redundancy in CSS.
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3.43
We've seen how we can move CSS into the style section of our web page.
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4.38
We've even seen how we can move CSS to an entirely different file.
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4.15
However, what we haven't yet seen is how to deal with other types of redundancy.
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5.12
And so let's take a look at an example of that now.
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3
Let's imagine, for example, that I want to style
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2.31
multiple different elements in different ways, but using some common properties.
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6.28
So, for example, let me create a new file that I'll, in this case,
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2.75
call variables.html.
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2.49
And you'll see why in a moment.
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1.86
I'll go ahead and copy hello.html, but I'll get rid
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2.58
of all this Bootstrap inside of it.
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2.81
Let's imagine that here I have in maybe two list, an ordered list
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4.67
and an unordered list, where my unordered list has
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5.07
an ordered item, maybe three unordered items,
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4.11
and my ordered list also has three ordered items.
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5.25
Again, just for sake of demonstration, I'm
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1.86
showing that we have these two lists now.
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2.13
And I'll open up variables.html just to give you
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3.42
a sense for what that could look like.
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3.09
We have three unordered items in an unordered list,
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2.82
three ordered items in our ordered list.
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3.09
Let's imagine I wanted to style these a little bit differently.
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3.28
Maybe inside the style section of my page
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2.33
I want to style the unordered list to have a font size of 14 pixels
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5.13
and maybe a color of red.
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2.34
And my ordered list, I would like that to have a font size of maybe larger, 18
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4.47
pixels, but also a color of red.
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2.2
I want to keep the same color for all the text,
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2.3
but I want the font sizes to be different.
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2.97
Now, if I refresh this page, here's what I see.
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2.19
They are indeed of different sizes.
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1.6
The ordered list items are larger than the unordered list items.
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3.71
And they're all red.
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1.66
But there was some redundancy, some repetition
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2.15
that was introduced when I was writing my CSS code.
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3
In particular when I was writing my CSS code,
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3.51
I've repeated this usage of the color red.
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2.7
If I ever want to change the color from red to blue, for example,
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2.88
I'm going to have to change my code in two different places.
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3.66
Ultimately, I'd just like for my CSS to be a little bit more powerful.
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4.28
And so that brings us to our last topic today, which is a language called Sass.
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4.54
And Sass is a language that is essentially an extension to CSS.
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3.78
It adds additional features to what CSS has
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2.46
to offer, just to make it a little bit more
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1.98
powerful for us to be able to use and manipulate CSS in a way that's
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3.72
going to be faster and remove some of the repetition
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3.33
that we might have had in CSS previously.
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2.58
And one of the key features of Sass is the ability to have variables.
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5.26
So let's take a look at an example of this now.
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2.6
I'm going to create a new file, normally when we created our CSS files,
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3.6
we called them like variables.css, something
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3
dot CSS to stand for a CSS file.
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3.12
Sass is a different language, though.
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2.04
So it's going to require a different extension.
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2.22