Details

Functions, mixins, variables, and placeholders should be declared with all lowercase letters and hyphens instead of underscores.

Bad: uppercase characters

$myVar: 10px;

@mixin myMixin() {
  ...
}

Good: all lowercase with hyphens

$my-var: 10px;

@mixin my-mixin() {
  ...
}

The Sass parser automatically treats underscores and hyphens the same, so even if you're using a library that declares a function with an underscore, you can refer to it using the hyphenated form instead.

Depending on whether you use underscores to denote private functions within your code, you can set the allow_leading_underscore option (enabled by default) which will ignore leading underscores in names if they exist, allowing declarations like @function _private-function() { ... }. If you want to further enforce a private naming convention, use PrivateNamingConvention.