CSS Protips

A collection of tips to help take your CSS skills pro.

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Table of Contents

• Protips
• Support
• Translations
• Contribution Guidelines

Protips

1. Use a CSS Reset
2. Inherit box-sizing
3. Use unset Instead of Resetting All Properties
4. Use :not() to Apply/Unapply Borders on Navigation
5. Check If Font Is Installed Locally
6. Add line-height to body
7. Set :focus for Form Elements
8. Vertically-Center Anything
9. Comma-Separated Lists
10. Select Items Using Negative nth-child
11. Use SVG for Icons
12. Use the "Lobotomized Owl" Selector
13. Use max-height for Pure CSS Sliders
14. Equal-Width Table Cells
15. Get Rid of Margin Hacks With Flexbox
16. Use Attribute Selectors with Empty Links
17. Style "Default" Links
18. Intrinsic Ratio Boxes
19. Style Broken Images
20. Use rem for Global Sizing; Use em for Local Sizing
21. Hide Autoplay Videos That Aren't Muted
22. Use :root for Flexible Type
23. Set font-size on Form Elements for a Better Mobile Experience
24. Use Pointer Events to Control Mouse Events
25. Set display: none on Line Breaks Used as Spacing

Use a CSS Reset

CSS resets help enforce style consistency across different browsers with a clean slate for styling elements. You can use a CSS reset library like Normalize, et al., or you can use a more simplified reset approach:

*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

Now elements will be stripped of margins and padding, and box-sizing lets you manage layouts with the CSS box model.

Demo

Note: If you follow the Inherit box-sizing tip below you might opt to not include the box-sizing property in your CSS reset.

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Inherit box-sizing

Let box-sizing be inherited from html:

html {
  box-sizing: border-box;
}

*,
*::before,
*::after {
  box-sizing: inherit;
}

This makes it easier to change box-sizing in plugins or other components that leverage other behavior.

Demo

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Use unset Instead of Resetting All Properties

When resetting an element's properties, it's not necessary to reset each individual property:

button {
  background: none;
  border: none;
  color: inherit;
  font: inherit;
  outline: none;
  padding: 0;
}

You can specify all of an element's properties using the all shorthand. Setting the value to unset changes an element's properties to their initial values:

button {
  all: unset;
}

Note: the all and unset shorthand isn't supported in IE11.

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Use :not() to Apply/Unapply Borders on Navigation

Instead of putting on the border...

/* add border */
.nav li {
  border-right: 1px solid #666;
}

...and then taking it off the last element...

/* remove border */
.nav li:last-child {
  border-right: none;
}

...use the :not() pseudo-class to only apply to the elements you want:

.nav li:not(:last-child) {
  border-right: 1px solid #666;
}

Here, the CSS selector is read as a human would describe it.

Demo

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Check If Font Is Installed Locally

You can check if a font is installed locally before fetching it remotely, which is a good performance tip, too.

@font-face {
  font-family: "Dank Mono";
  src:
    /* Full name */
    local("Dank Mono"),
    /* Postscript name */
    local("Dank Mono"),
    /* Otherwise, download it! */
    url("//...a.server/fonts/DankMono.woff");
}

code {
  font-family: "Dank Mono", system-ui-monospace;
}

H/T to Adam Argyle for sharing this protip and demo.

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Add line-height to body

You don't need to add line-height to each <p>, <h*>, et al. separately. Instead, add it to body:

body {
  line-height: 1.5;
}

This way textual elements can inherit from body easily.

Demo

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Set :focus for Form Elements

Sighted keyboard users rely on focus to determine where keyboard events go in the page. Make focus for form elements stand out and consistent then a browser's default implementation:

a:focus,
button:focus,
input:focus,
select:focus,
textarea:focus {
  box-shadow: none;
  outline: #000 dotted 2px;
  outline-offset: .05em;
}

Demo

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Vertically-Center Anything

No, it's not black magic, you really can center elements vertically. You can do this with flexbox...

html,
body {
  height: 100%;
  margin: 0;
}

body {
  -webkit-align-items: center;
  -ms-flex-align: center;
  align-items: center;
  display: -webkit-flex;
  display: flex;
}

...and also with CSS Grid:

body {
  display: grid;
  height: 100vh;
  margin: 0;
  place-items: center center;
}

Want to center something else? Vertically, horizontally...anything, anytime, anywhere? CSS-Tricks has a nice write-up on doing all of that.

Note: Watch for some buggy behavior with flexbox in IE11.

Demo

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Comma-Separated Lists

Make list items look like a real, comma-separated list:

ul > li:not(:last-child)::after {
  content: ",";
}

Use the :not() pseudo-class and no comma will be added to the last item.

Note: This tip may not be ideal for accessibility, specifically screen readers. And copy/paste from the browser doesn't work with CSS-generated content. Proceed with caution.

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Select Items Using Negative nth-child

Use negative nth-child in CSS to select items 1 through n.

li {
  display: none;
}

/* select items 1 through 3 and display them */
li:nth-child(-n+3) {
  display: block;
}

Or, since you've already learned a little about using :not(), try:

/* select all items except the first 3 and display them */
li:not(:nth-child(-n+3)) {
  display: block;
}

Demo

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Use SVG for Icons

There's no reason not to use SVG for icons:

.logo {
  background: url("logo.svg");
}

SVG scales well for all resolution types and is supported in all browsers back to IE9. Ditch your .png, .jpg, or .gif-jif-whatev files.

Note: If you have SVG icon-only buttons for sighted users and the SVG fails to load, this will help maintain accessibility:

.no-svg .icon-only::after {
  content: attr(aria-label);
}

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Use the "Lobotomized Owl" Selector

It may have a strange name but using the universal selector (*) with the adjacent sibling selector (+) can provide a powerful CSS capability:

* + * {
  margin-top: 1.5em;
}

In this example, all elements in the flow of the document that follow other elements will receive margin-top: 1.5em.

For more on the "lobotomized owl" selector, read Heydon Pickering's post on A List Apart.

Demo

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Use max-height for Pure CSS Sliders

Implement CSS-only sliders using max-height with overflow hidden:

.slider {
  max-height: 200px;
  overflow-y: hidden;
  width: 300px;
}

.slider:hover {
  max-height: 600px;
  overflow-y: scroll;
}

The element expands to the max-height value on hover and the slider displays as a result of the overflow.

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Equal-Width Table Cells

Tables can be a pain to work with. Try using table-layout: fixed to keep cells at equal width:

.calendar {
  table-layout: fixed;
}

Pain-free table layouts.

Demo

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Get Rid of Margin Hacks With Flexbox

When working with column gutters you can get rid of nth-, first-, and last-child hacks by using flexbox's space-between property:

.list {
  display: flex;
  justify-content: space-between;
}

.list .person {
  flex-basis: 23%;
}

Now column gutters always appear evenly-spaced.

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Use Attribute Selectors with Empty Links

Display links when the <a> element has no text value but the href attribute has a link:

a[href^="http"]:empty::before {
  content: attr(href);
}

That's pretty convenient.

Demo

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Style "Default" Links

Add a style for "default" links:

a[href]:not([class]) {
  color: #008000;
  text-decoration: underline;
}

Now links that are inserted via a CMS, which don't usually have a class attribute, will have a distinction without generically affecting the cascade.

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Intrinsic Ratio Boxes

To create a box with an intrinsic ratio, all you need to do is apply top or bottom padding to a div:

.container {
  height: 0;
  padding-bottom: 20%;
  position: relative;
}

.container div {
  border: 2px dashed #ddd;
  height: 100%;
  left: 0;
  position: absolute;
  top: 0;
  width: 100%;
}

Using 20% for padding makes the height of the box equal to 20% of its width. No matter the width of the viewport, the child div will keep its aspect ratio (100% / 20% = 5:1).

Demo

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Style Broken Images

Make broken images more aesthetically-pleasing with a little bit of CSS:

img {
  display: block;
  font-family: sans-serif;
  font-weight: 300;
  height: auto;
  line-height: 2;
  position: relative;
  text-align: center;
  width: 100%;
}

Now add pseudo-elements rules to display a user message and URL reference of the broken image:

img::before {
  content: "We're sorry, the image below is broken :(";
  display: block;
  margin-bottom: 10px;
}

img::after {
  content: "(url: " attr(src) ")";
  display: block;
  font-size: 12px;
}

Learn more about styling for this pattern in Ire Aderinokun's original post.

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Use rem for Global Sizing; Use em for Local Sizing

After setting the base font size at the root (html { font-size: 100%; }), set the font size for textual elements to em:

h2 {
  font-size: 2em;
}

p {
  font-size: 1em;
}

Then set the font-size for modules to rem:

article {
  font-size: 1.25rem;
}

aside .module {
  font-size: .9rem;
}

Now each module becomes compartmentalized and easier to style, more maintainable, and flexible.

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Hide Autoplay Videos That Aren't Muted

This is a great trick for a custom user stylesheet. Avoid overloading a user with sound from a video that autoplays when the page is loaded. If the sound isn't muted, don't show the video:

video[autoplay]:not([muted]) {
  display: none;
}

Once again, we're taking advantage of using the :not() pseudo-class.

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Use :root for Flexible Type

The type font size in a responsive layout should be able to adjust with each viewport. You can calculate the font size based on the viewport height and width using :root:

:root {
  font-size: calc(1vw + 1vh + .5vmin);
}

Now you can utilize the root em unit based on the value calculated by :root:

body {
  font: 1rem/1.6 sans-serif;
}

Demo

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Set font-size on Form Elements for a Better Mobile Experience

To avoid mobile browsers (iOS Safari, et al.) from zooming in on HTML form elements when a <select> drop-down is tapped, add font-size to the selector rule:

input[type="text"],
input[type="number"],
select,
textarea {
  font-size: 16px;
}

💃

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Use Pointer Events to Control Mouse Events

Pointer events allow you to specify how the mouse interacts with the element it's touching. To disable the default pointer event on a button, for instance:

.button-disabled {
  opacity: .5;
  pointer-events: none;
}

It's that simple.

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Set display: none on Line Breaks Used as Spacing

As Harry Roberts pointed out, this can help prevent CMS users from using extra line breaks for spacing:

br + br {
  display: none;
}

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Support

Current versions of Chrome, Firefox, Safari, Opera, Edge, and IE11.

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