diff --git a/components/style/properties/longhands/counters.mako.rs b/components/style/properties/longhands/counters.mako.rs
index db035568c71..2ad0f72cd4a 100644
--- a/components/style/properties/longhands/counters.mako.rs
+++ b/components/style/properties/longhands/counters.mako.rs
@@ -29,7 +29,7 @@ ${helpers.predefined_type(
 
 ${helpers.predefined_type(
     "counter-reset",
-    "CounterSetOrReset",
+    "CounterReset",
     engines="gecko servo-2013",
     initial_value="Default::default()",
     animation_value_type="discrete",
@@ -39,7 +39,7 @@ ${helpers.predefined_type(
 
 ${helpers.predefined_type(
     "counter-set",
-    "CounterSetOrReset",
+    "CounterSet",
     engines="gecko",
     initial_value="Default::default()",
     animation_value_type="discrete",
diff --git a/components/style/values/computed/counters.rs b/components/style/values/computed/counters.rs
index 1ae46c772ab..fd5e915c4a8 100644
--- a/components/style/values/computed/counters.rs
+++ b/components/style/values/computed/counters.rs
@@ -7,13 +7,17 @@
 use crate::values::computed::image::Image;
 use crate::values::generics::counters as generics;
 use crate::values::generics::counters::CounterIncrement as GenericCounterIncrement;
-use crate::values::generics::counters::CounterSetOrReset as GenericCounterSetOrReset;
+use crate::values::generics::counters::CounterReset as GenericCounterReset;
+use crate::values::generics::counters::CounterSet as GenericCounterSet;
 
 /// A computed value for the `counter-increment` property.
 pub type CounterIncrement = GenericCounterIncrement<i32>;
 
-/// A computed value for the `counter-set` and `counter-reset` properties.
-pub type CounterSetOrReset = GenericCounterSetOrReset<i32>;
+/// A computed value for the `counter-reset` property.
+pub type CounterReset = GenericCounterReset<i32>;
+
+/// A computed value for the `counter-set` property.
+pub type CounterSet = GenericCounterSet<i32>;
 
 /// A computed value for the `content` property.
 pub type Content = generics::GenericContent<Image>;
diff --git a/components/style/values/computed/mod.rs b/components/style/values/computed/mod.rs
index 955a1b93877..25103b34772 100644
--- a/components/style/values/computed/mod.rs
+++ b/components/style/values/computed/mod.rs
@@ -52,7 +52,7 @@ pub use self::box_::{ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness, Scro
 pub use self::box_::{TouchAction, VerticalAlign, WillChange};
 pub use self::color::{Color, ColorOrAuto, ColorPropertyValue, ColorScheme};
 pub use self::column::ColumnCount;
-pub use self::counters::{Content, ContentItem, CounterIncrement, CounterSetOrReset};
+pub use self::counters::{Content, ContentItem, CounterIncrement, CounterReset, CounterSet};
 pub use self::easing::TimingFunction;
 pub use self::effects::{BoxShadow, Filter, SimpleShadow};
 pub use self::flex::FlexBasis;
diff --git a/components/style/values/generics/counters.rs b/components/style/values/generics/counters.rs
index 2a8f70c8f44..e5656faea56 100644
--- a/components/style/values/generics/counters.rs
+++ b/components/style/values/generics/counters.rs
@@ -12,6 +12,8 @@ use crate::values::generics::CounterStyle;
 use crate::values::specified::Attr;
 use crate::values::CustomIdent;
 use std::ops::Deref;
+use std::fmt::{self, Write};
+use style_traits::{CssWriter, ToCss};
 
 /// A name / value pair for counters.
 #[derive(
@@ -21,7 +23,6 @@ use std::ops::Deref;
     PartialEq,
     SpecifiedValueInfo,
     ToComputedValue,
-    ToCss,
     ToResolvedValue,
     ToShmem,
 )]
@@ -31,9 +32,35 @@ pub struct GenericCounterPair<Integer> {
     pub name: CustomIdent,
     /// The value of the counter / increment / etc.
     pub value: Integer,
+    /// If true, then this represents `reversed(name)`.
+    /// NOTE: It can only be true on `counter-reset` values.
+    pub is_reversed: bool,
 }
 pub use self::GenericCounterPair as CounterPair;
 
+impl<Integer> ToCss for CounterPair<Integer>
+where
+    Integer: ToCss + PartialEq<i32>,
+{
+    fn to_css<W>(&self, dest: &mut CssWriter<W>) -> fmt::Result
+    where
+        W: Write,
+    {
+        if self.is_reversed {
+            dest.write_str("reversed(")?;
+        }
+        self.name.to_css(dest)?;
+        if self.is_reversed {
+            dest.write_str(")")?;
+            if self.value == i32::min_value() {
+                return Ok(());
+            }
+        }
+        dest.write_str(" ")?;
+        self.value.to_css(dest)
+    }
+}
+
 /// A generic value for the `counter-increment` property.
 #[derive(
     Clone,
@@ -48,7 +75,7 @@ pub use self::GenericCounterPair as CounterPair;
     ToShmem,
 )]
 #[repr(transparent)]
-pub struct GenericCounterIncrement<I>(pub GenericCounters<I>);
+pub struct GenericCounterIncrement<I>(#[css(field_bound)] pub GenericCounters<I>);
 pub use self::GenericCounterIncrement as CounterIncrement;
 
 impl<I> CounterIncrement<I> {
@@ -68,7 +95,7 @@ impl<I> Deref for CounterIncrement<I> {
     }
 }
 
-/// A generic value for the `counter-set` and `counter-reset` properties.
+/// A generic value for the `counter-set` property.
 #[derive(
     Clone,
     Debug,
@@ -82,18 +109,52 @@ impl<I> Deref for CounterIncrement<I> {
     ToShmem,
 )]
 #[repr(transparent)]
-pub struct GenericCounterSetOrReset<I>(pub GenericCounters<I>);
-pub use self::GenericCounterSetOrReset as CounterSetOrReset;
+pub struct GenericCounterSet<I>(#[css(field_bound)] pub GenericCounters<I>);
+pub use self::GenericCounterSet as CounterSet;
 
-impl<I> CounterSetOrReset<I> {
-    /// Returns a new value for `counter-set` / `counter-reset`.
+impl<I> CounterSet<I> {
+    /// Returns a new value for `counter-set`.
     #[inline]
     pub fn new(counters: Vec<CounterPair<I>>) -> Self {
-        CounterSetOrReset(Counters(counters.into()))
+        CounterSet(Counters(counters.into()))
     }
 }
 
-impl<I> Deref for CounterSetOrReset<I> {
+impl<I> Deref for CounterSet<I> {
+    type Target = [CounterPair<I>];
+
+    #[inline]
+    fn deref(&self) -> &Self::Target {
+        &(self.0).0
+    }
+}
+
+/// A generic value for the `counter-reset` property.
+#[derive(
+    Clone,
+    Debug,
+    Default,
+    MallocSizeOf,
+    PartialEq,
+    SpecifiedValueInfo,
+    ToComputedValue,
+    ToCss,
+    ToResolvedValue,
+    ToShmem,
+)]
+#[repr(transparent)]
+pub struct GenericCounterReset<I>(#[css(field_bound)] pub GenericCounters<I>);
+pub use self::GenericCounterReset as CounterReset;
+
+impl<I> CounterReset<I> {
+    /// Returns a new value for `counter-reset`.
+    #[inline]
+    pub fn new(counters: Vec<CounterPair<I>>) -> Self {
+        CounterReset(Counters(counters.into()))
+    }
+}
+
+impl<I> Deref for CounterReset<I> {
     type Target = [CounterPair<I>];
 
     #[inline]
@@ -119,7 +180,9 @@ impl<I> Deref for CounterSetOrReset<I> {
 )]
 #[repr(transparent)]
 pub struct GenericCounters<I>(
-    #[css(iterable, if_empty = "none")] crate::OwnedSlice<GenericCounterPair<I>>,
+    #[css(field_bound)]
+    #[css(iterable, if_empty = "none")]
+    crate::OwnedSlice<GenericCounterPair<I>>,
 );
 pub use self::GenericCounters as Counters;
 
diff --git a/components/style/values/specified/counters.rs b/components/style/values/specified/counters.rs
index aa442549fa5..c9507ce8383 100644
--- a/components/style/values/specified/counters.rs
+++ b/components/style/values/specified/counters.rs
@@ -21,6 +21,18 @@ use cssparser::{Parser, Token};
 use selectors::parser::SelectorParseErrorKind;
 use style_traits::{KeywordsCollectFn, ParseError, SpecifiedValueInfo, StyleParseErrorKind};
 
+#[derive(PartialEq)]
+enum CounterType { Increment, Set, Reset, }
+
+impl CounterType {
+    fn default_value(&self) -> i32 {
+        match *self {
+            Self::Increment => 1,
+            Self::Reset | Self::Set => 0,
+        }
+    }
+}
+
 /// A specified value for the `counter-increment` property.
 pub type CounterIncrement = generics::GenericCounterIncrement<Integer>;
 
@@ -29,26 +41,38 @@ impl Parse for CounterIncrement {
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
-        Ok(Self::new(parse_counters(context, input, 1)?))
+        Ok(Self::new(parse_counters(context, input, CounterType::Increment)?))
     }
 }
 
-/// A specified value for the `counter-set` and `counter-reset` properties.
-pub type CounterSetOrReset = generics::GenericCounterSetOrReset<Integer>;
+/// A specified value for the `counter-set` property.
+pub type CounterSet = generics::GenericCounterSet<Integer>;
 
-impl Parse for CounterSetOrReset {
+impl Parse for CounterSet {
     fn parse<'i, 't>(
         context: &ParserContext,
         input: &mut Parser<'i, 't>,
     ) -> Result<Self, ParseError<'i>> {
-        Ok(Self::new(parse_counters(context, input, 0)?))
+        Ok(Self::new(parse_counters(context, input, CounterType::Set)?))
+    }
+}
+
+/// A specified value for the `counter-reset` property.
+pub type CounterReset = generics::GenericCounterReset<Integer>;
+
+impl Parse for CounterReset {
+    fn parse<'i, 't>(
+        context: &ParserContext,
+        input: &mut Parser<'i, 't>,
+    ) -> Result<Self, ParseError<'i>> {
+        Ok(Self::new(parse_counters(context, input, CounterType::Reset)?))
     }
 }
 
 fn parse_counters<'i, 't>(
     context: &ParserContext,
     input: &mut Parser<'i, 't>,
-    default_value: i32,
+    counter_type: CounterType,
 ) -> Result<Vec<CounterPair<Integer>>, ParseError<'i>> {
     if input
         .try_parse(|input| input.expect_ident_matching("none"))
@@ -60,8 +84,14 @@ fn parse_counters<'i, 't>(
     let mut counters = Vec::new();
     loop {
         let location = input.current_source_location();
-        let name = match input.next() {
-            Ok(&Token::Ident(ref ident)) => CustomIdent::from_ident(location, ident, &["none"])?,
+        let (name, is_reversed) = match input.next() {
+            Ok(&Token::Ident(ref ident)) => (CustomIdent::from_ident(location, ident, &["none"])?, false),
+            Ok(&Token::Function(ref name)) if counter_type == CounterType::Reset && name.eq_ignore_ascii_case("reversed") => {
+                input.parse_nested_block(|input| {
+                    let location = input.current_source_location();
+                    Ok((CustomIdent::from_ident(location, input.expect_ident()?, &["none"])?, true))
+                })?
+            }
             Ok(t) => {
                 let t = t.clone();
                 return Err(location.new_unexpected_token_error(t));
@@ -69,10 +99,19 @@ fn parse_counters<'i, 't>(
             Err(_) => break,
         };
 
-        let value = input
-            .try_parse(|input| Integer::parse(context, input))
-            .unwrap_or(Integer::new(default_value));
-        counters.push(CounterPair { name, value });
+        let value = match input.try_parse(|input| Integer::parse(context, input)) {
+            Ok(start) =>
+                if start.value == i32::min_value() {
+                    // The spec says that values must be clamped to the valid range,
+                    // and we reserve i32::min_value() as an internal magic value.
+                    // https://drafts.csswg.org/css-lists/#auto-numbering
+                    Integer::new(i32::min_value() + 1)
+                } else {
+                    start
+                },
+            _ => Integer::new(if is_reversed { i32::min_value() } else { counter_type.default_value() }),
+        };
+        counters.push(CounterPair { name, value, is_reversed });
     }
 
     if !counters.is_empty() {
diff --git a/components/style/values/specified/mod.rs b/components/style/values/specified/mod.rs
index 64bc063960e..4aeee691566 100644
--- a/components/style/values/specified/mod.rs
+++ b/components/style/values/specified/mod.rs
@@ -44,7 +44,7 @@ pub use self::box_::{ScrollSnapAlign, ScrollSnapAxis, ScrollSnapStrictness, Scro
 pub use self::box_::{TouchAction, TransitionProperty, VerticalAlign, WillChange};
 pub use self::color::{Color, ColorOrAuto, ColorPropertyValue, ColorScheme};
 pub use self::column::ColumnCount;
-pub use self::counters::{Content, ContentItem, CounterIncrement, CounterSetOrReset};
+pub use self::counters::{Content, ContentItem, CounterIncrement, CounterReset, CounterSet};
 pub use self::easing::TimingFunction;
 pub use self::effects::{BoxShadow, Filter, SimpleShadow};
 pub use self::flex::FlexBasis;
@@ -577,6 +577,12 @@ impl One for Integer {
     }
 }
 
+impl PartialEq<i32> for Integer {
+    fn eq(&self, value: &i32) -> bool {
+        self.value() == *value
+    }
+}
+
 impl Integer {
     /// Trivially constructs a new `Integer` value.
     pub fn new(val: CSSInteger) -> Self {