diff --git a/src/value/css_function.rs b/src/value/css_function.rs
new file mode 100644
index 0000000..8d62094
--- /dev/null
+++ b/src/value/css_function.rs
@@ -0,0 +1,77 @@
+use std::iter::Peekable;
+
+use crate::error::SassResult;
+use crate::scope::Scope;
+use crate::selector::Selector;
+use crate::utils::{devour_whitespace, parse_interpolation};
+use crate::Token;
+
+pub(crate) fn eat_calc_args<I: Iterator<Item = Token>>(
+    toks: &mut Peekable<I>,
+    scope: &Scope,
+    super_selector: &Selector,
+) -> SassResult<String> {
+    let mut string = String::from("(");
+    let mut nesting = 0;
+    while let Some(tok) = toks.next() {
+        match tok.kind {
+            ' ' | '\t' | '\n' => {
+                devour_whitespace(toks);
+                string.push(' ');
+            }
+            '#' => {
+                if toks.peek().is_some() && toks.peek().unwrap().kind == '{' {
+                    toks.next();
+                    string.push_str(&parse_interpolation(toks, scope, super_selector)?.to_string());
+                } else {
+                    string.push('#');
+                }
+            }
+            '(' => {
+                nesting += 1;
+                string.push('(');
+            }
+            ')' => {
+                if nesting == 0 {
+                    break;
+                } else {
+                    nesting -= 1;
+                    string.push(')');
+                }
+            }
+            c => string.push(c),
+        }
+    }
+    string.push(')');
+    Ok(string)
+}
+
+#[allow(dead_code)]
+pub(crate) fn is_special_function(s: &str) -> bool {
+    s.starts_with("calc(")
+        || s.starts_with("var(")
+        || s.starts_with("env(")
+        || s.starts_with("min(")
+        || s.starts_with("max(")
+}
+
+pub(crate) fn eat_progid<I: Iterator<Item = Token>>(
+    toks: &mut Peekable<I>,
+    scope: &Scope,
+    super_selector: &Selector,
+) -> SassResult<String> {
+    let mut string = String::new();
+    while let Some(tok) = toks.next() {
+        match tok.kind {
+            'a'..='z' | 'A'..='Z' | '.' => {
+                string.push(tok.kind);
+            }
+            '(' => {
+                string.push_str(&eat_calc_args(toks, scope, super_selector)?);
+                break;
+            }
+            _ => return Err("expected \"(\".".into()),
+        }
+    }
+    Ok(string)
+}
diff --git a/src/value/mod.rs b/src/value/mod.rs
index 009fe52..97f3da9 100644
--- a/src/value/mod.rs
+++ b/src/value/mod.rs
@@ -11,6 +11,7 @@ pub(crate) use map::SassMap;
 pub(crate) use number::Number;
 pub(crate) use sass_function::SassFunction;
 
+mod css_function;
 mod map;
 mod number;
 mod ops;
diff --git a/src/value/parse.rs b/src/value/parse.rs
index 61e2387..f658be8 100644
--- a/src/value/parse.rs
+++ b/src/value/parse.rs
@@ -6,6 +6,8 @@ use num_bigint::BigInt;
 use num_rational::BigRational;
 use num_traits::pow;
 
+use super::css_function::{eat_calc_args, eat_progid};
+
 use crate::args::eat_call_args;
 use crate::builtin::GLOBAL_FUNCTIONS;
 use crate::color::Color;
@@ -360,6 +362,12 @@ impl Value {
         super_selector: &Selector,
     ) -> SassResult<IntermediateValue> {
         let mut s = eat_ident(toks, scope, super_selector)?;
+        if s == "progid" && toks.peek().is_some() && toks.peek().unwrap().kind == ':' {
+            toks.next();
+            s.push(':');
+            s.push_str(&eat_progid(toks, scope, super_selector)?);
+            return Ok(IntermediateValue::Value(Value::Ident(s, QuoteKind::None)));
+        }
         match toks.peek() {
             Some(Token { kind: '(', .. }) => {
                 toks.next();
@@ -374,10 +382,18 @@ impl Value {
                             )?))
                         }
                         None => {
-                            s.push_str(
-                                &eat_call_args(toks, scope, super_selector)?
-                                    .to_css_string(scope, super_selector)?,
-                            );
+                            match s.as_str() {
+                                "calc" | "element" | "expression" => {
+                                    s.push_str(&eat_calc_args(toks, scope, super_selector)?)
+                                }
+                                // "min" => {}
+                                // "max" => {}
+                                // "url" => {}
+                                _ => s.push_str(
+                                    &eat_call_args(toks, scope, super_selector)?
+                                        .to_css_string(scope, super_selector)?,
+                                ),
+                            }
                             return Ok(IntermediateValue::Value(Value::Ident(s, QuoteKind::None)));
                         }
                     },
diff --git a/tests/special-functions.rs b/tests/special-functions.rs
new file mode 100644
index 0000000..b02684a
--- /dev/null
+++ b/tests/special-functions.rs
@@ -0,0 +1,134 @@
+#![cfg(test)]
+
+#[macro_use]
+mod macros;
+
+test!(
+    calc_whitespace,
+    "a {\n  color: calc(       1      );\n}\n",
+    "a {\n  color: calc( 1 );\n}\n"
+);
+test!(
+    calc_multiple_args,
+    "a {\n  color: calc(1, 2, a, b, c);\n}\n"
+);
+test!(
+    calc_does_not_evaluate_arithmetic,
+    "a {\n  color: calc(1 + 2);\n}\n"
+);
+test!(
+    calc_evaluates_interpolated_arithmetic,
+    "a {\n  color: calc(#{1 + 2});\n}\n",
+    "a {\n  color: calc(3);\n}\n"
+);
+test!(
+    #[ignore]
+    calc_retains_silent_comment,
+    "a {\n  color: calc(//);\n}\n"
+);
+test!(
+    calc_retains_multiline_comment,
+    "a {\n  color: calc(/**/);\n}\n"
+);
+test!(calc_nested_parens, "a {\n  color: calc((((()))));\n}\n");
+test!(
+    element_whitespace,
+    "a {\n  color: element(       1      );\n}\n",
+    "a {\n  color: element( 1 );\n}\n"
+);
+test!(
+    element_multiple_args,
+    "a {\n  color: element(1, 2, a, b, c);\n}\n"
+);
+test!(
+    element_does_not_evaluate_arithmetic,
+    "a {\n  color: element(1 + 2);\n}\n"
+);
+test!(
+    element_evaluates_interpolated_arithmetic,
+    "a {\n  color: element(#{1 + 2});\n}\n",
+    "a {\n  color: element(3);\n}\n"
+);
+test!(
+    #[ignore]
+    element_retains_silent_comment,
+    "a {\n  color: element(//);\n}\n"
+);
+test!(
+    element_retains_multiline_comment,
+    "a {\n  color: element(/**/);\n}\n"
+);
+test!(
+    element_nested_parens,
+    "a {\n  color: element((((()))));\n}\n"
+);
+test!(
+    expression_whitespace,
+    "a {\n  color: expression(       1      );\n}\n",
+    "a {\n  color: expression( 1 );\n}\n"
+);
+test!(
+    expression_multiple_args,
+    "a {\n  color: expression(1, 2, a, b, c);\n}\n"
+);
+test!(
+    expression_does_not_evaluate_arithmetic,
+    "a {\n  color: expression(1 + 2);\n}\n"
+);
+test!(
+    expression_evaluates_interpolated_arithmetic,
+    "a {\n  color: expression(#{1 + 2});\n}\n",
+    "a {\n  color: expression(3);\n}\n"
+);
+test!(
+    #[ignore]
+    expression_retains_silent_comment,
+    "a {\n  color: expression(//);\n}\n"
+);
+test!(
+    expression_retains_multiline_comment,
+    "a {\n  color: expression(/**/);\n}\n"
+);
+test!(
+    expression_nested_parens,
+    "a {\n  color: expression((((()))));\n}\n"
+);
+test!(
+    progid_whitespace,
+    "a {\n  color: progid:(       1      );\n}\n",
+    "a {\n  color: progid:( 1 );\n}\n"
+);
+test!(
+    progid_multiple_args,
+    "a {\n  color: progid:(1, 2, a, b, c);\n}\n"
+);
+test!(
+    progid_does_not_evaluate_arithmetic,
+    "a {\n  color: progid:(1 + 2);\n}\n"
+);
+test!(
+    progid_evaluates_interpolated_arithmetic,
+    "a {\n  color: progid:(#{1 + 2});\n}\n",
+    "a {\n  color: progid:(3);\n}\n"
+);
+test!(
+    #[ignore]
+    progid_retains_silent_comment,
+    "a {\n  color: progid:(//);\n}\n"
+);
+test!(
+    progid_retains_multiline_comment,
+    "a {\n  color: progid:(/**/);\n}\n"
+);
+test!(
+    progid_nested_parens,
+    "a {\n  color: progid:((((()))));\n}\n"
+);
+test!(
+    progid_values_after_colon,
+    "a {\n  color: progid:apple.bottoM..jeans.boots();\n}\n"
+);
+error!(
+    progid_number_after_colon,
+    "a {\n  color: progid:ap1ple.bottoM..jeans.boots();\n}\n", "Error: expected \"(\"."
+);