CSS Variables

css

http://www.phpied.com/css-variables/
http://www.sitepoint.com/css-variables-land-firefox-31/
https://www.sitepoint.com/practical-guide-css-variables-custom-properties/
https://madebymike.com.au/writing/using-css-variables/

How can we use CSS variables?

The good news is that the learning curve for CSS variables is really shallow and they're straightforward to use. A CSS variable looks like this:

:root { --main-color: red; }

.your-element { color: var(--main-color); }

Whenever you want to color something red, you can use var(—main-color), and when you want to change from red to green or any other color, just update the value of the —main-color variable and all the instances where you have applied the variable will change accordingly.