url()

The url() function is commonly used in CSS, but its syntax is different than other functions: it can take either a quoted or unquoted URL. Because an unquoted URL isn’t a valid SassScript expression, Sass needs special logic to parse it.

If the url()’s argument is a valid unquoted URL, Sass parses it as-is, although interpolation may also be used to inject SassScript values. If it’s not a valid unquoted URL—for example, if it contains variables or function calls—it’s parsed as a normal plain CSS function call.

$roboto-font-path: "../fonts/roboto";

@font-face {
    // This is parsed as a normal function call that takes a quoted string.
    src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2");

    font-family: "Roboto";
    font-weight: 100;
}

@font-face {
    // This is parsed as a normal function call that takes an arithmetic
    // expression.
    src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2");

    font-family: "Roboto";
    font-weight: 300;
}

@font-face {
    // This is parsed as an interpolated special function.
    src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2");

    font-family: "Roboto";
    font-weight: 400;
}

$roboto-font-path: "../fonts/roboto"

@font-face
    // This is parsed as a normal function call that takes a quoted string.
    src: url("#{$roboto-font-path}/Roboto-Thin.woff2") format("woff2")

    font-family: "Roboto"
    font-weight: 100


@font-face
    // This is parsed as a normal function call that takes an arithmetic
    // expression.
    src: url($roboto-font-path + "/Roboto-Light.woff2") format("woff2")

    font-family: "Roboto"
    font-weight: 300


@font-face
    // This is parsed as an interpolated special function.
    src: url(#{$roboto-font-path}/Roboto-Regular.woff2) format("woff2")

    font-family: "Roboto"
    font-weight: 400

@font-face {
  src: url("../fonts/roboto/Roboto-Thin.woff2") format("woff2");
  font-family: "Roboto";
  font-weight: 100;
}
@font-face {
  src: url("../fonts/roboto/Roboto-Light.woff2") format("woff2");
  font-family: "Roboto";
  font-weight: 300;
}
@font-face {
  src: url(../fonts/roboto/Roboto-Regular.woff2) format("woff2");
  font-family: "Roboto";
  font-weight: 400;
}

calc(), element(), progid:...(), and expression()

The calc() and element() functions are defined in the CSS spec. Because calc()’s mathematical expressions conflict with Sass’s arithmetic, and element()’s IDs could be parsed as colors, they need special parsing.

expression() and functions beginning with progid: are legacy Internet Explorer features that use non-standard syntax. Although they’re no longer supported by recent browsers, Sass continues to parse them for backwards compatibility.

Sass allows any text in these function calls, including nested parentheses. Nothing is interpreted as a SassScript expression, with the exception that interpolation can be used to inject dynamic values.

.logo {
  $width: 800px;
  width: $width;
  position: absolute;
  left: calc(50% - #{$width / 2});
  top: 0;
}

.logo
  $width: 800px
  width: $width
  position: absolute
  left: calc(50% - #{$width / 2})
  top: 0

.logo {
  width: 800px;
  position: absolute;
  left: calc(50% - 400px);
  top: 0;
}

min() and max()

Compatibility:

Dart Sass

since 1.11.0

LibSass

✗

Ruby Sass

✗

▶

CSS added support for min() and max() functions in Values and Units Level 4, from where they were quickly adopted by Safari to support the iPhoneX. But Sass supported its own min() and max() functions long before this, and it needed to be backwards-compatible with all those existing stylesheets. This led for the need for extra-special syntactic cleverness.

If a min() or max() function call is valid plain CSS, it will be compiled to a CSS min() or max() call. “Plain CSS” includes nested calls to calc(), env(), var(), min(), or max(), as well as interpolation. As soon as any part of the call contains a SassScript feature like variables or function calls, though, it’s parsed as a call to Sass’s core min() or max() function instead.

$padding: 12px;

.post {
  // Since these max() calls don't use any Sass features other than
  // interpolation, they're compiled to CSS max() calls.
  padding-left: max(#{$padding}, env(safe-area-inset-left));
  padding-right: max(#{$padding}, env(safe-area-inset-right));
}

.sidebar {
  // Since these refer to a Sass variable without interpolation, they call
  // Sass's built-in max() function.
  padding-left: max($padding, 20px);
  padding-right: max($padding, 20px);
}

$padding: 12px

.post
  // Since these max() calls don't use any Sass features other than
  // interpolation, they're compiled to CSS max() calls.
  padding-left: max(#{$padding}, env(safe-area-inset-left))
  padding-right: max(#{$padding}, env(safe-area-inset-right))


.sidebar
  // Since these refer to a Sass variable without interpolation, they call
  // Sass's built-in max() function.
  padding-left: max($padding, 20px)
  padding-right: max($padding, 20px)

.post {
  padding-left: max(12px, env(safe-area-inset-left));
  padding-right: max(12px, env(safe-area-inset-right));
}

.sidebar {
  padding-left: 20px;
  padding-right: 20px;
}