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

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1. Use a CSS Reset
2. Inherit box-sizing
3. Use :not() to Apply/Unapply Borders on Navigation
4. Add line-height to body
5. Vertically-Center Anything
6. Comma-Separated Lists
7. Select Items Using Negative nth-child
8. Use SVG for Icons
9. Use the "Lobotomized Owl" Selector
10. Use max-height for Pure CSS Sliders
11. Equal-Width Table Cells
12. Get Rid of Margin Hacks With Flexbox
13. Use Attribute Selectors with Empty Links
14. Style "Default" Links
15. Consistent Vertical Rhythm
16. Intrinsic Ratio Boxes
17. Style Broken Images
18. Use rem for Global Sizing; Use em for Local Sizing
19. Hide Autoplay Videos That Aren't Muted
20. Use :root for Flexible Type
21. Set font-size on Form Elements for a Better Mobile Experience

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

* {
 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.

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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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.

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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;
}

Sure, you can use .nav li + li or even .nav li:first-child ~ li, but with :not() the intent is very clear and the CSS selector defines the border the way a human would describe it.

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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.

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No, it's not black magic, you really can center elements vertically:

html, body {
 height: 100%;
 margin: 0;
}
body {
 -webkit-align-items: center;
 -ms-flex-align: center;
 align-items: center;
 display: -webkit-flex;
 display: flex;
}

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.

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

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

Use the :not() pseudo-class so no comma is 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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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 items 1 through 3 and display them */
li:not(:nth-child(-n+3)) {
 display: none;
}

Well that was pretty easy.

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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. So 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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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.

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

.calendar {
 table-layout: fixed;
}

Pain-free table layouts.

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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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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.

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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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Use a universal selector (*) within an element to create a consistent vertical rhythm:

.intro > * {
 margin-bottom: 1.25rem;
}

Consistent vertical rhythm provides a visual aesthetic that makes content far more readable.

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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).

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

img {
 display: block;
 font-family: Helvetica, Arial, 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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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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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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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;
}

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

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