postcss-rem 
PostCSS plugin to use rem units with optional pixel fallback. Based on sass-rem.
See also: startijenn-rem, vanilla JavaScript version.
Example
Input
.demo {
font-size: rem(24px); /* Simple */
padding: rem(5px 10px); /* Multiple values */
margin: rem(10px 0.5rem); /* Existing rem */
border-bottom: rem(1px solid black); /* Multiple mixed values */
box-shadow: rem(
0 0 2px #ccc,
inset 0 0 5px #eee
); /* Comma-separated values */
text-shadow: rem(1px 1px) #eee, rem(-1px) 0 #eee; /* Alternate use */
}Output
.demo {
font-size: 1.5rem; /* Simple */
padding: 0.3125rem 0.625rem; /* Multiple values */
margin: 0.625rem 0.5rem; /* Existing rem */
border-bottom: 0.0625rem solid black; /* Multiple mixed values */
box-shadow: 0 0 0.125rem #ccc, inset 0 0 0.3125rem #eee; /* Comma-separated values */
text-shadow: 0.0625rem 0.0625rem #eee, -0.0625rem 0 #eee; /* Alternate use */
}Options
With baseline to 10 (html { font-size: 62.5%; }) and fallback to true:
.demo {
font-size: 24px;
font-size: 2.4rem; /* Simple */
padding: 5px 10px;
padding: 0.5rem 1rem; /* Multiple values */
margin: 10px 5px;
margin: 1rem 0.5rem; /* Existing rem */
border-bottom: 1px solid black;
border-bottom: 0.1rem solid black; /* Multiple mixed values */
box-shadow: 0 0 2px #ccc, inset 0 0 5px #eee;
box-shadow: 0 0 0.2rem #ccc, inset 0 0 0.5rem #eee; /* Comma-separated values */
text-shadow: 1px 1px #eee, -1px 0 #eee;
text-shadow: 0.1rem 0.1rem #eee, -0.1rem 0 #eee; /* Alternate use */
}With convert to px (for a lt-ie9 only stylesheet for example):
.demo {
font-size: 24px; /* Simple */
padding: 5px 10px; /* Multiple values */
margin: 10px 8px; /* Existing rem */
border-bottom: 1px solid black; /* Multiple mixed values */
box-shadow: 0 0 2px #ccc, inset 0 0 5px #eee; /* Comma-separated values */
text-shadow: 1px 1px #eee, -1px 0 #eee; /* Alternate use */
}Usage
Install with npm i postcss-rem and use with PostCSS:
postcss([require("postcss-rem")]);Example with custom options:
postcss([
require("postcss-rem")({
name: "to-rem", // Default to 'rem'
baseline: 10, // Default to 16
// convert: "px", // Default to 'rem'
fallback: true, // Default to false
precision: 6, // Default to 5
}),
]);See PostCSS docs for examples for your environment.