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Learn how to use Bootstrap to quickly add styling to your website! 

Learn Bootstrap 4: Utilities and Components

In arenas and stadiums, there are giant screens called _jumbotrons_ which display the main event for everyone in the crowd to see. Bootstrap also offers a jumbotron component that serves a similar function and makes content stand out. 

Here's an example of a basic jumbotron that only contains text: 
```html
<div class="jumbotron">
  <h1>Wow this stands out!</h1>
</div>
```

In the example above we included an `<h1>` element, but we could add images or a variety of Bootstrap components. Look over <a href="https://getbootstrap.com/docs/4.2/components/jumbotron" target="_blank" rel="noopener noreferrer">Bootstrap's jumbotron documentation</a> for more elaborate examples. 



The Jumbotron Component

Another common component we see on websites are buttons. Buttons represent a clickable object that does something else in return like navigating to a different page, submitting a form, or opening a popup, just to name a few. 

By default, the `<button>` element doesn't have much styling. But, with Bootstrap we can make button components that have more styling. Here's an example from <a href="https://getbootstrap.com/docs/4.2/components/buttons/#examples" target="_blank" rel="noopener noreferrer">Bootstrap's button documentation</a> : 

```html
<button type="button" class="btn btn-danger">Danger</button>
``` 

The example above will render a red button that has the text `Danger` inside the button:
* It has a `type` of `"button"`.
* It has two classes, `"btn"` and `"btn-danger"`.
  * The `"btn"` class provides Bootstrap's default button styling.
  * The  `"btn-danger"` turns the button red and conveys the purpose of the button, i.e. clicking this button might not be safe! 

Visit <a href="https://getbootstrap.com/docs/4.2/components/buttons" target="_blank" rel="noopener noreferrer">Bootstrap's button documentation</a> for a comprehensive list of how to create and use button components. 

We'll add some interactivity and make the buttons do something in the following exercises. For now, let's practice creating Bootstrap button components.


The Button Component

There are times that we want to showcase a group of images but not want to have our users scroll through one picture on top of another. Instead, we could fit our images into a slideshow using Bootstrap's _carousel component_. 

<a href="https://getbootstrap.com/docs/4.2/components/carousel/" target="_blank" rel="noopener noreferrer">Bootstrap has many carousel examples</a> but let's go through a basic example together: 

```html
<div id="carouselExampleSlidesOnly" class="carousel slide" data-ride="carousel">
  <div class="carousel-inner">
    <div class="carousel-item active">
      <img class="d-block w-100" src="example_slide_1.png" alt="First slide">
    </div>
    <div class="carousel-item">
      <img class="d-block w-100" src="example_slide_2.png" alt="Second slide">
    </div>
  </div>
</div>
```

The example above will render a slideshow that loops through two images, displaying one at a time. In the actual code:
* The parent `<div>` element has an `id` of `"carouselExampleSlidesOnly"`, two classes `"carousel"` and `"slide"`, and the attribute `data-ride="carousel"`.
  * The `id` is used later when we want to add controls to click between slides.
  * The classes provide the styling and formatting.
  * The `data-ride` attribute provides the interactivity and slide transitions.
* We also have a nested `<div class="carousel-inner">` element that contains other `<div>` elements with images.
* Nested inside the 2nd `<div>` is yet another `<div>` with a class of `"carousel-item"` and `"active"` (only one image needs the active class, if none have active, no images are shown).
* Each `<div>` with `.carousel-item` has a nested `<img>` element which have the usual `src` and `alt` attributes.    
  * The `<img>` elements use two utility classes`"d-block"` sets its display as block and the `"w-100"`  is to take up 100% of the width. 

Now, let's implement a carousel with arrows that control the slideshow.


The Carousel Component

If we want to style and format text, we can use <a href="https://getbootstrap.com/docs/4.2/utilities/text/" target="_blank" rel="noopener noreferrer">Bootstrap's text utility classes</a>.

For instance, if we want our text to be bold, we could add a class of `"font-weight-bold"` like so:
```html
<p class="font-weight-bold">
  This rendered text is bold.
</p>
```

We can also combine Bootstrap classes for additional styling. Let's say we wanted our text to also be uppercased. We would add `"text-uppercase"` to the class attribute:
```html
<p class="font-weight-bold text-uppercase">
  This rendered text is both bold and uppercased. 
</p>
```

Let's make use of these text utility classes!


Styling Text

Bootstrap also allows us to quickly add interactivity to a webpage. One way to include interactivity is to toggle the visibility of an element. 

To add such a feature, we need two elements and a few attributes &mdash; one element with content and another element that switches the visibility of the previous element. For example:

```html
<button class="btn btn-primary" type="button" data-toggle="collapse" data-target="#collapseExample" aria-expanded="false" aria-controls="collapseExample">
  This button controls the following div's visibility. 
</button>

<div class="collapse" id="collapseExample">
  <p>This content's visibility gets toggled</p>
</div>
```

In the example above, we have a `<button>` element that toggles the visibility of the `<div>` element below it. 

The button has an attribute `data-toggle="collapse"` which enables button's toggle ability. Another attribute, `data-target="#collapseExample"`, means that this button toggles the visibility of the element with the `id` of  `"collapseExample"`. The `aria-expanded` and `aria-controls` attributes are information for screen readers and other accessibility means. 

Focusing our attention on the `<div>` below the button, notice that it has a class of  `"collapse"`, which hides the content when the webpage initially renders. Our `<div>` also has an `id` of `"collapseExample"` which corresponds to the value of the button's `data-target`. 

With both elements set up, we've made our page interactive! Look up <a href="https://getbootstrap.com/docs/4.2/components/collapse/" target="_blank" rel="noopener noreferrer">Bootstrap's collapse documentation</a> for additional ways of incorporating collapse. 


Collapsing a Component

Bootstrap utility classes provide an element with styling and purpose. Let's get acquainted with utility classes by styling the color of our elements. 

Let's say we want to change the text color of our paragraph element from the default black to blue. We would add a class of `"text-primary"`, like so:
```html
<p class="text-primary">This text is blue!</p>
```

According to the documentation, the `"text"` portion of the class targets the element's text styling. Appending `"primary"` after `"text"` changes the text color to blue. The name of the class, `"text-primary"`, also signifies that this `<p>` element conveys information that appears first, i.e, is the primary text. 

We could have used any of the classes provided in <a href="https://getbootstrap.com/docs/4.2/utilities/colors/#color" target="_blank" rel="noopener noreferrer">Bootstrap's color example</a> to change the text color of our `<p>` element.

Similarly, we can also change the background color:
```html
<div class="bg-success">
  Green! This signifies success! 
</div>
```

In the example above, we've assigned the `<div>` element a class of `"bg-success"`. The `"bg"` part references the element's background and `"success"` changes the background color to green. We can also tell from the name of the class that this `<div>` element is meant to be used when something happened/worked. We can find more background utility classes at
<a href="https://getbootstrap.com/docs/4.2/utilities/colors/#background-color" target="_blank" rel="noopener noreferrer">Bootstrap's background color examples</a>. 

To get the full range of what we can do with Bootstrap's color utility classes, check out <a href="https://getbootstrap.com/docs/4.2/utilities/colors/" target="_blank" rel="noopener noreferrer">Bootstrap's colors documentation</a>. Now, let's add some color to our own examples.


Adding Colors

Let's combine our knowledge of collapse, buttons, and the nav component to make a responsive navbar! We often find navbars at the top of websites and we can use a navbar to quickly navigate to useful/important pages on the website. 

Below is an example from <a href="https://getbootstrap.com/docs/4.2/components/navbar/#supported-content" target="_blank" rel="noopener noreferrer">Bootstrap's Navbar documentation</a> that we've modified: 

```html
<nav class="navbar navbar-expand-lg navbar-light bg-light">
  <a class="navbar-brand" href="#">Brand Goes Here</a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>
  
  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav">
      <li class="nav-item active">
        <a class="nav-link" href="#">Current Page Link <span class="sr-only">(current)</span></a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Another Page Link</a>
      </li>
    </ul>
  </div>
</nav>
```

There's a lot going on, so let's break it down before we use it in our own code:
* We have a `<nav>` element with multiple classes:
  * `"navbar"` makes this `<nav>` a Bootstrap navbar. 
  * `"navbar-expand-lg"` renders the `<div class="collapse navbar-collapse">` element on large (and extra large screens). The `"lg"` portion is called a _breakpoint_ and refers to screen size widths. We can append one of any <a href="https://getbootstrap.com/docs/4.2/layout/grid/#grid-options" target="_blank" rel="noopener noreferrer">breakpoint value</a> at the end, i.e. `"sm"`, `"md"`, `"lg"`, or `"xl"`. 
  * `"navbar-light"` assigns a color scheme to the navbar.
  * `"bg-light"` assigns a background color to the navbar. 
* Inside the `<nav>` is an `<a>` with a class of `"navbar-brand"` which can be an image or text that represents the brand/logo of the website.
* There is a `<button>` that renders when a user's screen size is smaller than the breakpoint value in `"navbar-expand-{breakpoint}"` and toggles the visibility of the navbar menu to save space. 
  * If the user's screen size matches the breakpoint (or is bigger), then the `<div>`, with the nav component and its links, renders instead of the button.  
* The `<ul>` and the nested `<li>` make up a nav component.
* The first `<li>` has a class of `"active"` which highlights the user's current page. 


Creating a Navbar

The Bootstrap framework allows us to streamline webpage layout and styling. In this lesson, we're going to focus on using Bootstrap's utility classes that provide additional styling and components that each serve distinct purposes.

Throughout this lesson, we're going to become acquainted with Bootstrap's extensive documentation. Bootstrap's documentation offers a lot of important information and examples. For instance, we can follow Bootstrap's <a href="https://getbootstrap.com/docs/4.2/getting-started/introduction/#starter-template" target="_blank" rel="noopener noreferrer">Getting Started - Starter template</a> to add the Bootstrap framework to our project! 

After we've incorporated the necessary Bootstrap files, we can quickly style our elements using Bootstrap's predefined CSS classes and take advantage of Bootstrap's JavaScript files to incorporate a level of interactivity to our webpages. 

Now that we've got the basics covered, we can bootstrap up our site! 


Bootstrap Utilities and Components

Go ahead and give yourself that well-deserved pat on the back, you've worked your way through Bootstrap utility classes and components! 

Remember, it is **extremely important** to check Bootstrap documentation for instructions on component implementation! 

Because we checked documentation we were able to use:
* animations and interactivity that requires the addition of Bootstrap's JavaScript files.
* utility classes which affect the styling and position of elements.
* the nav component provides default Bootstrap styling to links.
* the responsive navbar component to quickly navigate between webpages. 
* the jumbotron component which prominently displays an image or text.
* the card component that acts as a stylized content container. 
* collapse to toggle component visibility.
* the carousel component to create a slideshow which displays images or text.

Now, go forth and see what else you can bootstrap to your site! 


Review

When considering the layout of a webpage, we have to think about how to position our elements. Conveniently, Bootstrap provides positioning utility classes. 

We can apply CSS positioning styling by assigning an element a utility class found in <a href="https://getbootstrap.com/docs/4.2/utilities/position" target="_blank" rel="noopener noreferrer">Bootstrap's positioning documentation</a>. It would also be worth knowing <a href="https://developer.mozilla.org/en-US/docs/Web/CSS/position" target="_blank" rel="noopener noreferrer">how these position are rendered on a webpage</a>. 

For example, if we want an element that is fixed to the top, we can apply a `"fixed-top"` class:  
```html
<div class="fixed-top">
  This div will be fixed at the top of the screen. 
</div>
```

There are a few other positioning utility classes, so let's explore how to use them!



Element Positioning

In addition to useful utility classes, Bootstrap offers a collection of _components_, such as a navbar, buttons, a carousel/slideshow for images, and much more! Each Bootstrap component serves a distinct purpose and we can find examples and code snippets directly from the documentation &mdash; then, we can tweak the components to our personal needs. 

The first component we'll investigate is the _navigation (nav) component_ which offers our users a collection of links. The nav component is slightly different from a _navbar_ component. The nav component is often specific to one or a few webpages, whereas a navbar often appears on all the pages of a website. 

There are many ways to create a basic nav component. Here's one example:

```html
<ul class="nav">
  <li class="nav-item">
    <a class="nav-link" href="#">First Link</a>
  </li>
  <li class="nav-item">
    <a class="nav-link" href="#">Second Link</a>
  </li>
</ul>
``` 
In the above example:
* We created a navigation component using an `<ul>` that has a class of `"nav"`. 
* The `<ul>` has nested `<li>` elements which each have a class of `"nav-item"`. 
* Inside each `<li>` is an `<a>` which has a class of `"nav-link"`. 

Alternatively, for a simpler nav component of only links:
```html
<nav class="nav">
  <a class="nav-link" href="#">First Link</a>
  <a class="nav-link" href="#">Second Link</a>
</nav>
```
Notice that we still have the parent element with a class of `"nav"` and the children elements with a class of `"nav-link"`. Both examples render the same links, but we might choose one example over the other depending on how we want our layout to look. 

Read through <a href="https://getbootstrap.com/docs/4.2/components/navs/" target="_blank" rel="noopener noreferrer">Bootstrap's nav documentation</a> for more information.


The Navigation Component

Bootstrap also has a _card component_ that serves as a container for smaller customized content. Card components are often grouped together to display a collection of similar content in manageable chunks. We can draw a comparison of the card component to playing cards in deck &mdash; in both cases, there are cards grouped together and each one contains something different.  

Below is an example modified from <a href="https://getbootstrap.com/docs/4.2/components/card/#example" target="_blank" rel="noopener noreferrer">Bootstrap's card documentation</a>:

```html
<div class="card">
  <img class="card-img-top" src="placeholder.jpg" alt="card example image">
  <div class="card-body">
    <h5 class="card-title">Card title</h5>
    <p class="card-text">Card description goes here.</p>
    <a href="#" class="card-link">Link to somewhere.</a>
  </div>
</div>
```

Let's highlight a few key points from the example:
* To make a card component we need to assign a class of `"card"` to an element.
* Inside the card component, there are two children, an `<img>` and a `<div>` element.
* The `<img>` has a class of `"card-img-top"` which adds styling and formatting to the image.
* The `<div>` has a class of `"card-body"` which adds a section with default padding.
* The content inside the card body all have classes with `"card-{value}"` which adds styling to these elements specific for Bootstrap cards.
*  By default, this card will take up the entire width of its parent element. 

Let's add some of our own cards, remember to check <a href="https://getbootstrap.com/docs/4.2/components/card/#example" target="_blank" rel="noopener noreferrer">Bootstrap's card documentation</a> for more customizations! 
