CSS Media Queries

Problem Statement

The key to designing and building responsive layouts is having your content respond to the size of the device (or "medium"). Your CSS can query the "media" (plural of "medium") to find out their sizes and proportions. These "media queries" are the focus of this lesson. By writing "media queries" you can can ensure your site looks great on all devices.

Objectives

1. What is the purpose of media queries

2. What is the media query syntax

3. Where should "breakpoints" be created

What is the Purpose of Media Queries?

Media queries are a feature of CSS. They are sets of styles that are applied when the medium satisfies specific conditions. Media queries most frequently decide whether a group of CSS rules applies based on the device "viewport" (or, "screen") size. The points at which the layout adjusts, based on some media property (or properties!), is called a "breakpoint".

What is the Media Query Syntax?

Below are a few examples of syntax for writing a media query statement within our CSS code:

@media (max-width: 992px) {
  body {
    background-color: blue;
  }
}

Below are more specific and complete examples of the media query syntax:

@media screen and (max-width: 992px) {
  body {
    background-color: blue;
  }
}

@media only screen and (max-width: 992px) {
  body {
    background-color: blue;
  }
}

When defining a media query, we use the @media keyword followed by conditional statements that will trigger the media query to apply or not. Below we will break down each property available in media queries:

not, only

The logical keywords "not" or "only" can be used optionally to include or exclude specific media types or screen sizes. For instance, we may want to specify that a navigation bar should extend across the width of our page, but only on screens larger than 800px in height. It might also be the case that you want a CSS rule to apply to all devices, but not screens smaller than 400px wide.

@media only screen and (max-width: 992px) {
  body {
    background-color: blue;
  }
}

@media not screen and (max-width: 992px) {
  body {
    background-color: blue;
  }
}

mediatype

Currently, the only well-supported media types are: screen, print, or all (meaning all devices). Mobile, tablet, and desktop devices all fall within the screen mediatype, while print is used for displaying content in a 'print preview' mode. Most commonly we are concerned only with screen.

@media [screen|print|all] and (max-width: 992px) {
  body {
    background-color: blue;
  }
}

and, ,

We can use and and , to separate or combine conditions.

• Using and requires that both conditions on each side of the and are true in order for the query to apply.

• Using , stands for or, meaning that only one of the conditions on either side of the comma has to be true for the query to trigger.

@media screen and (min-width: 992px) and (max-width: 1136px) {
  body {
    background-color: blue;
  }
}

@media screen and (min-width: 992px), (max-width: 1136px) {
  body {
    background-color: blue;
  }
}

(expression)

We define conditional expressions by writing the test and wrapping it in parentheses. The expression must evaluate to true in order for the query to trigger unless using a ,. These expressions are followed by a set of {} curly braces that enclose the CSS selectors and rules that will be applied when the media query is triggered.

@media (max-width: 992px) {
  body {
    background-color: blue;
  }
}

Usage

To give better context, let's create a media query that will change a paragraph's text from red to green when the screen size falls below 800px:

/* initial style */
p {
    color: red;
}

/* media query */
@media only screen and (max-width: 800px) {
  p {
    color: green;
  }
}

On the second line we provide some initial style that will be applied unless our media query triggers. We have set our paragraph to have red text. On line 5, we create a media query using @media and set it to only trigger for screen devices that have a max-width of 800px.

In other words, the style will only be applied on screens that are less than 801px wide. Following the condition are a pair of curly braces ({}) that enclose the style(s) to be applied when the condition is met. In our case, on screens that are 800px wide or less, we change the text color of paragraphs to green instead of red.

For our size conditions we can use the properties min-width, max-width, min-height, and max-height, all referring to the size of the device's viewport (i.e., the screen size). Above, we looked at max-width; now let's explore min-width:

/* initial style */
p {
  color: red;
}

/* media query */
@media only screen and (min-width: 400px) {
  p {
    color: green;
  }
}

On line 2, we set the default color of paragraphs to red again. On line 5, we set the terms of our media query — namely, that the width of the screen device must be 400px or more.

So, max-width triggers when a screen is smaller than the specified size, and min-width triggers when a screen is larger than a certain size.

As mentioned before, we can use the and keyword to chain multiple conditions together. Let's look at an example of that:

/* initial style */
p {
  color: red;
}

/* media query */
@media only screen and (min-width: 400px) and (max-width: 800px) {
   p {
     color: green;
   }
}

Here we are changing the text color to green only on screens that are between 400px and 800px.

One nice thing about media queries is that they automatically inherit all of the styles written outside of their {} braces. So inside the media query we only need to write the CSS for the properties we wish to change. With a set of different media queries, it is possible to have specific styling for mobile and desktop screen sizes, along with tablet screen sizes in between.

Where Should Break Points Be Created?

Let your content determine where break points should fall. Use Developer Tools and Emulators to discover where your content starts to break down. Then create an appropriate break point (media query at that width) to solve the issue. This will ensure that your content looks good on any and all devices not just the popular ones.

Advanced layout techniques, such as grid (which will be covered in later lessons), allow us to keep media query break points to a minimum. You can, for instance, set a media query for max-width: 414px, the width of the iPhone 6+, which will affect basically all mobile phones, but allow CSS grid to dynamically adjust the width of web page elements for smaller phones.

Conclusion

CSS Media Queries provide us a way to alter our CSS at specific screen sizes by setting breakpoints at different screen widths. Using the max-width condition expressions to trigger styles below a certain size and the min-width condition expressions to trigger styles above a certain size can help you build powerful, flexible interfaces for various screen sizes and devices. Instead of trying to target specific device sizes, use the in-browser dev tools for experimentation, and allow your unique content to determine at which sizes to write media query break points. Write media queries as you need them at whatever size your content starts to become unsightly.

Resources

• MDN - CSS - Media Queries
• CSS Tricks - Media Queries
• Simulate Mobile Devices with Device Mode in Google Chrome

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