58 lines
2.1 KiB
Markdown
58 lines
2.1 KiB
Markdown
---
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title: CSS Custom Properties
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---
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## CSS Custom Properties
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CSS custom properties are also referred to as CSS variables. As of October 2018, CSS custom properties are still an experimental technology. Consider [browser support](https://developer.mozilla.org/en-US/docs/Web/CSS/--*#Browser_compatibility) before using the feature in production.
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### Declaring Custom Properties
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Within a selector, custom properties are declared using two hyphens (--) and the name, followed by the value. The value can be simple, such as a color (RGB, hex code, etc.) or size (using pixel, em, rem, etc.), or it can be more complex, like a drop shadow definition. See the examples below.
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```css
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:root {
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--firstVariable: red;
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--headerSize: 16px;
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--dropShadow: 1px 1px 2px 2px rgba(100,100,100,0.2);
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```
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Declaring custom properties in the `:root` selector make those properties globally available. The `:root` selector can be considered the same as the `html` selector.
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### Using Custom Properties
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To use a custom property, the `var()` function is used, which takes a single argument of the custom property name.
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```css
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h1 {
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font-size: var(--headerSize);
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}
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.card {
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box-shadow: var(--dropShadow);
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}
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```
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### Cascading Custom Properties
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When custom properties are declared in the `:root` selector, those properties are globally available; any style rules can use the properties. If a custom property needs to be different for specific element, class, or id, a property of the same can be declared in that selector. The compiler will first look for a property name within the immediate enclosing selector, then move to the `:root`.
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```css
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:root {
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--font-color: red;
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}
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h1 {
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--font-color: blue;
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}
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h1 {
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font-color: var(--font-color); /* blue */
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}
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h2 {
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font-color: var(--font-color); /* red */
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}
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```
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#### More Information:
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For more information visit:
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- [MDN](https://developer.mozilla.org/en-US/docs/Web/CSS/--*)
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- [W3C Candidate Recommendation Document](https://www.w3.org/TR/css-variables/)
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- [Browser Support](https://caniuse.com/#feat=css-variables)
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- [A Practical Guide to CSS Variables(SitePoint)](https://www.sitepoint.com/practical-guide-css-variables-custom-properties/)
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