Sass offers functions and mixins that accept parameters. You can use Sass default parameters, that is, parameters that have a value even if you don’t provide them when the function or mixin is called.

Let’s focus on mixins here. Here’s the syntax of a mixin:

@mixin foo($a, $b, $c) {
// I can use $a, $b, and $c in here, but there is a risk they are null

.el {
@include foo(1, 2, 3);

// if I tried to do `@include foo;`
// … which is valid syntax…
// I’d get `Error: Missing argument $a.` from Sass

It’s safer and more useful to set up default parameters in this Sass mixin:

@mixin foo($a: 1, $b: 2, $c: 3) {

.el {
// Now this is fine
@include foo;

// AND I can send in params as well
@include foo(“three”, “little”, “pigs”);

But what if I wanted to send in $b and $c, but leave $a as the Sass default parameter? The trick is that you send in named parameters:

@mixin foo($a: 1, $b: 2, $c: 3) {

.el {
// Only sending in the second two params, $a will be the default.
@include foo($b: 2, $c: 3);

A real-life example using Sass default parameters

Here’s a quick-y mixin that outputs what you need for very basic styled scrollbars (Kitty has one as well):

@mixin scrollbars(
$size: 10px,
$foreground-color: #eee,
$background-color: #333
) {
// For Google Chrome
&::-webkit-scrollbar {
width: $size;
height: $size;
&::-webkit-scrollbar-thumb {
background: $foreground-color;
&::-webkit-scrollbar-track {
background: $background-color;

// Standard version (Firefox only for now)
scrollbar-color: $foreground-color $background-color;

Now I can call it like this:

.scrollable {
@include scrollbars;

.thick-but-otherwise-default-scrollable {
// I can skip $b and $c because they are second and third
@include scrollbars(30px);

.custom-colors-scrollable {
// I can skip the first param if all the others are named.
@include scrollbars($foreground-color: orange, $background-color: black);

.totally-custom-scrollable {
@include scrollbars(20px, red, black);

I’m just noting this as I had to search around a bit to figure this out. I was trying stuff like sending empty strings or null as the first parameter in order to “skip” it, but that doesn’t work. Gotta do the named parameter approach.

A Practical Tip For Using Sass Default Parameters originally published on CSS-Tricks. You should get the newsletter and become a supporter.