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Learn how to build web pages that are accessible to everyone using modern CSS techniques and accessibility standards.

Accessibility

Have you ever visited a website that seemed hard to use or navigate? Perhaps you couldn't tell if an element was interactive or couldn't read some of the text due to size issues. Chances are this has happened to you at least once, and it can be extremely frustrating. These problems that you encountered were likely the result of poor web accessibility.

Web accessibility is one of those aspects of web development where its presence, when implemented correctly, goes unnoticed, but its absence can destroy the user experience. There are a variety of considerations to make when making a website accessible, ranging from the size and color of the text to invisible properties that are processed by assistive tools such as screen readers.

Learning how to harness and apply the fundamental aspects of web accessibility should be a top priority for any developer looking to build an amazing, inclusive experience for all users.

Introduction to Web Accessibility

Text alignment and paragraph width on a page are important things to consider when creating the text layout. When there is too much space between words or the paragraph width is too wide, it makes the text difficult to read. We can avoid this by using the `text-align` and `width` properties to set appropriate values like the below example code.

```css
p {
  text-align: left;
  width: 400px;
}
```

Generally, it is recommended to align text using `left`, `right`, or `center` values. The `justify` value can also be used but can cause a decrease in readability because it creates uneven word spacing to create equal line lengths.

Paragraph width can also impact readability. It is recommended to have 45 to 85 characters per line, with the ideal being suggested as 65 characters. In the above example, we set the width using `px` as the unit of measure. A more appropriate unit for this purpose is the `ch` unit, with `1ch` being equivalent to the width of the zero (`0`) character. The `ch` unit also scales with changes in the value of the `font-family` or `font-size` property.

Visual Readability: Structure

So far, we have been very concerned with how our page looks on screens, but we haven't been considering the other ways in which users can consume the content of your web page. For example, how does the page look when printed? Luckily, there are some ways a page can be made more accessible, even when viewed on paper.

One way to do this is to use media queries, specifically the `@media print` query:

```css
@media print {
  nav {
    display: none;
  }
}
```

The above code snippet causes the `nav` element to be removed when the page is printed. This is useful for reducing clutter on the page, especially for elements with no real benefit from being present on paper as they cannot be accessed properly.

Print media queries can also be used to display values of elements that otherwise couldn't be understood. For example, we can display the value of the `href` attribute when printed so the user can still have access to the link. To expose an `href` in printed form, the following code can be used:

```css
@media print {
  a[href^="http"]:after {
    content: " (" attr(href) ")";
  }
}
```

Accessibility Across Mediums

An important consideration when applying CSS to a page is the relationship that the CSS stylesheet has with the HTML document's underlying structure. This relationship may not seem very important, but if mismanaged or ignored, it can have a huge impact on the accessibility and navigability of a web page.

Take a list of elements, for instance, that is styled to look like the image gallery below:

![Picture of image gallery (Pinterest-like layout)](https://static-assets.codecademy.com/Courses/Learn-CSS/Accessibility/gallery.png)

At first glance, this gallery seems fine, especially to users who do not have special accessibility needs, but any attempt to navigate this board without a mouse would say otherwise. The order of the elements visually is completely different from their order in the _DOM_. This will lead to an increased difficulty for a user using alternative navigation methods from navigating the page properly.

Additionally, screen readers process the order of the DOM, so it is possible to have a mismatch between what is visually presented and what is being read. In this case, the screen reader would read the elements seemingly out of order relative to how they are displayed on the page.

Due to these considerations, it is important to order the content on your page to make sense in the absence of styling. This will lead to a uniform experience for all users.

Design Reflecting Structure

Color plays a major role in a user's ability to read the information located on a page. If colors lack sufficient contrast, they can become hard to distinguish from one another. Oftentimes, text can become lost in the background color, which prevents users, especially those with vision impairments, from reading it. The solution to this is to provide adequate contrast between foreground and background elements. To understand contrast, we must first understand where it comes from: the color wheel.

![diagram of the color wheel](https://static-assets.codecademy.com/Courses/Learn-CSS/Accessibility/color-wheel.png)

Two colors are contrasting when they are from different segments of the color wheel. Thus, the farther apart the segments, the higher the contrast between the two colors. The difference between the two colors is known as the _contrast ratio_ and a minimum contrast ratio must be met in order to adhere to accessibility standards. The minimum contrast ratio denotes how high the contrast is between the text of certain sizes and width on a specific background. This ratio can range from 1:1, where both compared colors are the same, to 21:1, where the two colors are black and white.

![contrast ratio](https://static-assets.codecademy.com/Courses/Learn-CSS/Accessibility/contrast-ratio.png)

According to the [Web Content Accessibility Guidelines (WCAG)](https://www.w3.org/TR/WCAG20/), contrast ratios are classified using a 3-tier hierarchy:

* Level A is the minimum level.
* Level AA includes all Level A and AA requirements. Many organizations strive to meet Level AA.
* Level AAA includes all Level A, AA, and AAA requirements.

The recommended minimum contrast ratios between the background and its text using these standards are as follows:

* 4.5:1 (AA criteria)&mdash;Text that is less than `24px` (not bold) and `19px` (bold).
* 3:1 (AA criteria)&mdash;Text larger than `24px` (not bold) and `19px` (bold).
* 7:1 (AAA criteria)&mdash;Text that is less than `24px` (not bold) and `19px` (bold).
* 4.5:1 (AAA criteria)&mdash;Text larger than `24px` (not bold) and `19px` (bold).

There are a variety of tools that can be used to determine contrast ratios. The [Chrome Canary](https://www.google.com/chrome/canary/) browser has a built-in contrast ratio display inside its developer tools. Another popular stand-alone tool is [WebAIM](https://webaim.org/resources/contrastchecker/).

Visual Readability: Color

Color can also be used as a contextual indicator of intent or meaning. One simple way to convey additional information to the user using color is in the form of links. Many times, links will be present on web pages that will bring users to other sources of information. To let users know they have visited a link from your page previously, the `:visited` selector can be used.  This selector will apply styling to links that the user has already clicked. The most common style applied via this selector is a color change.

```css
a:visited {
  color: purple;
}
```

Navigation is another contextual use for color. When elements are focused, they will often have styling applied to denote where the focus is being applied.  This is critical for navigation, especially with modalities other than the mouse, such as the keyboard.  Without the `:focus` selector providing additional styling, often using color or shadowing to show focus, users would not know where they were on the page when navigating using means other than a mouse.

```css
input:focus {
  border-color: blue;
}
```

An additional common use case for contextual use of color is in the indication of success and error states. This can most often be seen in form validation, where accepted field values will turn an input green and rejected fields will be colored red.

![validation colors](https://static-assets.codecademy.com/Courses/Learn-CSS/Accessibility/validation.png)

Contextual Readability: Color

Font size has a large impact on the readability of content on a web page. If the font is too small or large, it can become difficult to read depending on the user's distance from the screen. Over time, the `font-size` property has increased to match these accessibility concerns&mdash;arising, in part, from the introduction of multi-size devices to the digital space, including Smart TVs, tablets, phones, etc. While the size of a web page's text largely depends on the typeface used, a minimum size between 18 to 20 pixels is recommended for smaller screen sizes.

Line height, or the spacing between lines of text, also contributes heavily to readability. If the `line-height` property's value is too small, lines will appear too close together. If the `line-height` is too large, lines will be separated by too much distance. The default value of `line-height` in browsers is around 1.2&mdash;however, [Web Content Accessibility Standards](https://www.w3.org/TR/2008/REC-WCAG20-20081211/#visual-audio-contrast-visual-presentation) recommend a minimum of 1.5 within paragraphs.

Lastly, the `letter-spacing` property provides additional visual clarity by controlling the space between individual letters in a word&mdash;the value of `letter-spacing` property defaults to `normal` in browsers.  Providing a value to this property (for example, `0.5em`) will expand or contract the space between letters.  Letter spacing is also accessible from screen readers' perspective as it allows characters to be spaced without the use of actual space characters (` `). Some screen readers will read each letter individually if spacing characters are used, which will make the text incomprehensible to users.

Visual Readability: Scale

Accessibility isn't only about being able to read text or see elements on a web page.  Another facet of accessibility is providing context clues to users to show them additional information about the elements they are viewing.  For instance, information or concepts comprised of multiple words is often abbreviated (e.g., CSS stands for _Cascading Style Sheets_).  As a provider of the information, a web page should make the full definition available to users.  This can be done using the `<abbr>` element. Hovering over the text contained in this element will display an alternative name for it to the user.

```html
<abbr title='Cascading Style Sheets'>CSS</abbr>
```

Another simple way to convey interactivity is with links. Styling links in a unique way allows users to discern them from other text that may surround them. One way to do this is by underlining links. It is generally advisable to leave underline styling on links to provide clarity.

```css
a {
  text-decoration: underline;
}
```

Plain text isn't the only source of information on pages, however. Interactive elements such as buttons can also exist.  To indicate that something is interactive on a page, users should be given contextual clues in addition to design-based clues.  The most common way to denote interactivity is with the cursor. Using the `cursor` property, the mouse cursor can be changed to show a visual representation of potential interactivity.

```css
.button {
  cursor: pointer;
}
```

Contextual Readability: Interactivity

Inevitably, at some point, a web page will need to hide content from users somehow. There are a variety of ways to do this, but each one has different use cases and implications.

The first way that content could be hidden is by hiding it from everyone. In this case, everyone refers to both human users viewing the web page and screen readers. To hide content from everyone in this manner, you can set [the `visibility` property](https://developer.mozilla.org/en-US/docs/Web/CSS/visibility) to `hidden` or set [the `display` property](https://developer.mozilla.org/en-US/docs/Web/CSS/display) to `none`. 

The second method is to hide content only visually. This means that content will still be accessible to screen readers, but not human users. This method is more complex as browser quirks can come into play, and considerations needing to be made around focusing the elements via things like keyboard navigation.

The third method is to hide the content semantically, hiding it from screen readers only but displaying it visually. This method is useful for obscuring content that provides no meaningful context to screen reader users, such as decorative icons and repeated text. This can be done by setting the `aria-hidden` HTML attribute to `'true'`:

```html
<p class='hidden-sentence' aria-hidden='true'>This is hidden from screen readers!</p>
```

Additionally, styling with specific values for `text-indent`, `font-size`, or `height` can produce the same result but with caveats.

Visibility

There are a lot of considerations to make when it comes to accessibility. Let's take some time to review the key considerations:

* Text should be at least `18px` in size, and paragraphs should have a `line-height` of at least 1.5 to increase the readability of content.
* Color contrast between elements should be at least 4.5:1 for standard font sizes.
* Interactive elements should have a visual appearance denoting interactivity, such as underlined links and pointer cursor.
* Abbreviated content should be given additional content via the `<abbr>` element.
* When hiding elements from users, use `visibility: hidden;` or `display: none;` to hide content from both assisted and non-assisted users.
* Visual display should reflect the structure of the presented elements within the HTML to provide navigational coherence for assisted and non-assisted users.
* Design pages for consumption in different mediums such as print.

The web has become a tool that many people use daily. Ensuring that this tool is accessible to as many people as possible should be strived for designing any web page. Next time you build a website, try and consider some of these points and incorporate them into your design!