diff --git a/eng/Dependencies.props b/eng/Dependencies.props
index a17d5470524..51caea76d33 100644
--- a/eng/Dependencies.props
+++ b/eng/Dependencies.props
@@ -21,6 +21,7 @@ and are generated based on the last package release.
 
   <ItemGroup Label=".NET team dependencies">
     <LatestPackageReference Include="Microsoft.Azure.SignalR" Version="$(MicrosoftAzureSignalRPackageVersion)" />
+    <LatestPackageReference Include="Microsoft.Css.Parser" Version="$(MicrosoftCssParserPackageVersion)" />
     <LatestPackageReference Include="Microsoft.CodeAnalysis.Common" Version="$(MicrosoftCodeAnalysisCommonPackageVersion)" />
     <LatestPackageReference Include="Microsoft.CodeAnalysis.CSharp.Workspaces" Version="$(MicrosoftCodeAnalysisCSharpWorkspacesPackageVersion)" />
     <LatestPackageReference Include="Microsoft.CodeAnalysis.CSharp" Version="$(MicrosoftCodeAnalysisCSharpPackageVersion)" />
diff --git a/eng/Versions.props b/eng/Versions.props
index 87e8509d883..c926d918c76 100644
--- a/eng/Versions.props
+++ b/eng/Versions.props
@@ -188,6 +188,7 @@
     <MicrosoftCodeAnalysisCommonPackageVersion>3.7.0-4.20351.7</MicrosoftCodeAnalysisCommonPackageVersion>
     <MicrosoftCodeAnalysisCSharpPackageVersion>3.7.0-4.20351.7</MicrosoftCodeAnalysisCSharpPackageVersion>
     <MicrosoftCodeAnalysisCSharpWorkspacesPackageVersion>3.7.0-4.20351.7</MicrosoftCodeAnalysisCSharpWorkspacesPackageVersion>
+    <MicrosoftCssParserPackageVersion>1.0.0-20200708.1</MicrosoftCssParserPackageVersion>
     <MicrosoftIdentityModelClientsActiveDirectoryPackageVersion>3.19.8</MicrosoftIdentityModelClientsActiveDirectoryPackageVersion>
     <MicrosoftIdentityModelLoggingPackageVersion>5.5.0</MicrosoftIdentityModelLoggingPackageVersion>
     <MicrosoftIdentityModelProtocolsOpenIdConnectPackageVersion>5.5.0</MicrosoftIdentityModelProtocolsOpenIdConnectPackageVersion>
diff --git a/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Application.cs b/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Application.cs
index 73a05d570f7..d4c57b799d5 100644
--- a/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Application.cs
+++ b/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Application.cs
@@ -40,6 +40,7 @@ namespace Microsoft.AspNetCore.Razor.Tools
             Commands.Add(new DiscoverCommand(this));
             Commands.Add(new GenerateCommand(this));
             Commands.Add(new BrotliCompressCommand(this));
+            Commands.Add(new RewriteCssCommand(this));
         }
 
         public CancellationToken CancellationToken { get; }
diff --git a/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Microsoft.AspNetCore.Razor.Tools.csproj b/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Microsoft.AspNetCore.Razor.Tools.csproj
index 1489542b024..a12f1b86246 100644
--- a/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Microsoft.AspNetCore.Razor.Tools.csproj
+++ b/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/Microsoft.AspNetCore.Razor.Tools.csproj
@@ -38,6 +38,7 @@
 
   <ItemGroup>
     <Reference Include="Newtonsoft.Json" Version="$(Razor_NewtonsoftJsonPackageVersion)" />
+    <Reference Include="Microsoft.Css.Parser" Version="$(MicrosoftCssParserPackageVersion)" />
   </ItemGroup>
 
   <ItemGroup>
diff --git a/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/RewriteCssCommand.cs b/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/RewriteCssCommand.cs
new file mode 100644
index 00000000000..70f57167eb0
--- /dev/null
+++ b/src/Razor/Microsoft.AspNetCore.Razor.Tools/src/RewriteCssCommand.cs
@@ -0,0 +1,277 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using System;
+using System.Collections.Generic;
+using System.IO;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using Microsoft.Css.Parser.Parser;
+using Microsoft.Css.Parser.Tokens;
+using Microsoft.Css.Parser.TreeItems;
+using Microsoft.Css.Parser.TreeItems.AtDirectives;
+using Microsoft.Css.Parser.TreeItems.Selectors;
+using Microsoft.Extensions.CommandLineUtils;
+
+namespace Microsoft.AspNetCore.Razor.Tools
+{
+    internal class RewriteCssCommand : CommandBase
+    {
+        public RewriteCssCommand(Application parent)
+            : base(parent, "rewritecss")
+        {
+            Sources = Option("-s", "Files to rewrite", CommandOptionType.MultipleValue);
+            Outputs = Option("-o", "Output file paths", CommandOptionType.MultipleValue);
+            CssScopes = Option("-c", "CSS scope identifiers", CommandOptionType.MultipleValue);
+        }
+
+        public CommandOption Sources { get; }
+
+        public CommandOption Outputs { get; }
+
+        public CommandOption CssScopes { get; }
+
+        protected override bool ValidateArguments()
+        {
+            if (Sources.Values.Count != Outputs.Values.Count)
+            {
+                Error.WriteLine($"{Sources.Description} has {Sources.Values.Count}, but {Outputs.Description} has {Outputs.Values.Count} values.");
+                return false;
+            }
+
+            if (Sources.Values.Count != CssScopes.Values.Count)
+            {
+                Error.WriteLine($"{Sources.Description} has {Sources.Values.Count}, but {CssScopes.Description} has {CssScopes.Values.Count} values.");
+                return false;
+            }
+
+            return true;
+        }
+
+        protected override Task<int> ExecuteCoreAsync()
+        {
+            Parallel.For(0, Sources.Values.Count, i =>
+            {
+                var source = Sources.Values[i];
+                var output = Outputs.Values[i];
+                var cssScope = CssScopes.Values[i];
+
+                var inputText = File.ReadAllText(source);
+                var rewrittenCss = AddScopeToSelectors(inputText, cssScope);
+                File.WriteAllText(output, rewrittenCss);
+            });
+
+            return Task.FromResult(ExitCodeSuccess);
+        }
+
+        // Public for tests
+        public static string AddScopeToSelectors(string inputText, string cssScope)
+        {
+            var cssParser = new DefaultParserFactory().CreateParser();
+            var stylesheet = cssParser.Parse(inputText, insertComments: false);
+
+            var resultBuilder = new StringBuilder();
+            var previousInsertionPosition = 0;
+
+            var scopeInsertionPositionsVisitor = new FindScopeInsertionPositionsVisitor(stylesheet);
+            scopeInsertionPositionsVisitor.Visit();
+            foreach (var (currentInsertionPosition, insertionType) in scopeInsertionPositionsVisitor.InsertionPositions)
+            {
+                resultBuilder.Append(inputText.Substring(previousInsertionPosition, currentInsertionPosition - previousInsertionPosition));
+                
+                switch (insertionType)
+                {
+                    case ScopeInsertionType.Selector:
+                        resultBuilder.AppendFormat("[{0}]", cssScope);
+                        break;
+                    case ScopeInsertionType.KeyframesName:
+                        resultBuilder.AppendFormat("-{0}", cssScope);
+                        break;
+                    default:
+                        throw new NotImplementedException($"Unknown insertion type: '{insertionType}'");
+                }
+
+                
+                previousInsertionPosition = currentInsertionPosition;
+            }
+
+            resultBuilder.Append(inputText.Substring(previousInsertionPosition));
+
+            return resultBuilder.ToString();
+        }
+
+        private static bool TryFindKeyframesIdentifier(AtDirective atDirective, out ParseItem identifier)
+        {
+            var keyword = atDirective.Keyword;
+            if (string.Equals(keyword?.Text, "keyframes", StringComparison.OrdinalIgnoreCase))
+            {
+                var nextSiblingText = keyword.NextSibling?.Text;
+                if (!string.IsNullOrEmpty(nextSiblingText))
+                {
+                    identifier = keyword.NextSibling;
+                    return true;
+                }
+            }
+
+            identifier = null;
+            return false;
+        }
+
+        private enum ScopeInsertionType
+        {
+            Selector,
+            KeyframesName,
+        }
+
+        private class FindScopeInsertionPositionsVisitor : Visitor
+        {
+            public List<(int, ScopeInsertionType)> InsertionPositions { get; } = new List<(int, ScopeInsertionType)>();
+
+            private readonly HashSet<string> _keyframeIdentifiers;
+
+            public FindScopeInsertionPositionsVisitor(ComplexItem root) : base(root)
+            {
+                // Before we start, we need to know the full set of keyframe names declared in this document
+                var keyframesIdentifiersVisitor = new FindKeyframesIdentifiersVisitor(root);
+                keyframesIdentifiersVisitor.Visit();
+                _keyframeIdentifiers = keyframesIdentifiersVisitor.KeyframesIdentifiers
+                    .Select(x => x.Text)
+                    .ToHashSet(StringComparer.Ordinal); // Keyframe names are case-sensitive
+            }
+
+            protected override void VisitSelector(Selector selector)
+            {
+                // For a ruleset like ".first child, .second { ... }", we'll see two selectors:
+                //   ".first child," containing two simple selectors: ".first" and "child"
+                //   ".second", containing one simple selector: ".second"
+                // Our goal is to insert immediately after the final simple selector within each selector
+                var lastSimpleSelector = selector.Children.OfType<SimpleSelector>().LastOrDefault();
+                if (lastSimpleSelector != null)
+                {
+                    InsertionPositions.Add((lastSimpleSelector.AfterEnd, ScopeInsertionType.Selector));
+                }
+            }
+
+            protected override void VisitAtDirective(AtDirective item)
+            {
+                // Whenever we see "@keyframes something { ... }", we want to insert right after "something"
+                if (TryFindKeyframesIdentifier(item, out var identifier))
+                {
+                    InsertionPositions.Add((identifier.AfterEnd, ScopeInsertionType.KeyframesName));
+                }
+                else
+                {
+                    VisitDefault(item);
+                }
+            }
+
+            protected override void VisitDeclaration(Declaration item)
+            {
+                switch (item.PropertyNameText)
+                {
+                    case "animation":
+                    case "animation-name":
+                        // The first two tokens are <propertyname> and <colon> (otherwise we wouldn't be here).
+                        // After that, any of the subsequent tokens might be the animation name.
+                        // Unfortunately the rules for determining which token is the animation name are very
+                        // complex - https://developer.mozilla.org/en-US/docs/Web/CSS/animation#Syntax
+                        // Fortunately we only want to rewrite animation names that are explicitly declared in
+                        // the same document (we don't want to add scopes to references to global keyframes)
+                        // so it's sufficient just to match known animation names.
+                        var animationNameTokens = item.Children.Skip(2).OfType<TokenItem>()
+                            .Where(x => x.TokenType == CssTokenType.Identifier && _keyframeIdentifiers.Contains(x.Text));
+                        foreach (var token in animationNameTokens)
+                        {
+                            InsertionPositions.Add((token.AfterEnd, ScopeInsertionType.KeyframesName));
+                        }
+                        break;
+                    default:
+                        // We don't need to do anything else with other declaration types
+                        break;
+                }
+            }
+        }
+
+        private class FindKeyframesIdentifiersVisitor : Visitor
+        {
+            public FindKeyframesIdentifiersVisitor(ComplexItem root) : base(root)
+            {
+            }
+
+            public List<ParseItem> KeyframesIdentifiers { get; } = new List<ParseItem>();
+
+            protected override void VisitAtDirective(AtDirective item)
+            {
+                if (TryFindKeyframesIdentifier(item, out var identifier))
+                {
+                    KeyframesIdentifiers.Add(identifier);
+                }
+                else
+                {
+                    VisitDefault(item);
+                }
+            }
+        }
+
+        private class Visitor
+        {
+            private readonly ComplexItem _root;
+
+            public Visitor(ComplexItem root)
+            {
+                _root = root ?? throw new ArgumentNullException(nameof(root));
+            }
+
+            public void Visit()
+            {
+                VisitDefault(_root);
+            }
+
+            protected virtual void VisitSelector(Selector item)
+            {
+                VisitDefault(item);
+            }
+
+            protected virtual void VisitAtDirective(AtDirective item)
+            {
+                VisitDefault(item);
+            }
+
+            protected virtual void VisitDeclaration(Declaration item)
+            {
+                VisitDefault(item);
+            }
+
+            protected virtual void VisitDefault(ParseItem item)
+            {
+                if (item is ComplexItem complexItem)
+                {
+                    VisitDescendants(complexItem);
+                }
+            }
+
+            private void VisitDescendants(ComplexItem container)
+            {
+                foreach (var child in container.Children)
+                {
+                    switch (child)
+                    {
+                        case Selector selector:
+                            VisitSelector(selector);
+                            break;
+                        case AtDirective atDirective:
+                            VisitAtDirective(atDirective);
+                            break;
+                        case Declaration declaration:
+                            VisitDeclaration(declaration);
+                            break;
+                        default:
+                            VisitDefault(child);
+                            break;
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/src/Razor/Microsoft.AspNetCore.Razor.Tools/test/RewriteCssCommandTest.cs b/src/Razor/Microsoft.AspNetCore.Razor.Tools/test/RewriteCssCommandTest.cs
new file mode 100644
index 00000000000..7a5b1122338
--- /dev/null
+++ b/src/Razor/Microsoft.AspNetCore.Razor.Tools/test/RewriteCssCommandTest.cs
@@ -0,0 +1,174 @@
+// Copyright (c) .NET Foundation. All rights reserved.
+// Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
+
+using Xunit;
+
+namespace Microsoft.AspNetCore.Razor.Tools
+{
+    public class RewriteCssCommandTest
+    {
+        [Fact]
+        public void HandlesEmptyFile()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(string.Empty, "TestScope");
+
+            // Assert
+            Assert.Equal(string.Empty, result);
+        }
+
+        [Fact]
+        public void AddsScopeAfterSelector()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .myclass { color: red; }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .myclass[TestScope] { color: red; }
+", result);
+        }
+
+        [Fact]
+        public void HandlesMultipleSelectors()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .first, .second { color: red; }
+    .third { color: blue; }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .first[TestScope], .second[TestScope] { color: red; }
+    .third[TestScope] { color: blue; }
+", result);
+        }
+
+        [Fact]
+        public void HandlesComplexSelectors()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .first div > li, body .second:not(.fancy)[attr~=whatever] { color: red; }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .first div > li[TestScope], body .second:not(.fancy)[attr~=whatever][TestScope] { color: red; }
+", result);
+        }
+
+        [Fact]
+        public void HandlesSpacesAndCommentsWithinSelectors()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .first /* space at end {} */ div , .myclass /* comment at end */ { color: red; }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .first /* space at end {} */ div[TestScope] , .myclass[TestScope] /* comment at end */ { color: red; }
+", result);
+        }
+
+        [Fact]
+        public void HandlesAtBlocks()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .myclass { color: red; }
+
+    @media only screen and (max-width: 600px) {
+        .another .thing {
+            content: 'This should not be a selector: .fake-selector { color: red }'
+        }
+    }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .myclass[TestScope] { color: red; }
+
+    @media only screen and (max-width: 600px) {
+        .another .thing[TestScope] {
+            content: 'This should not be a selector: .fake-selector { color: red }'
+        }
+    }
+", result);
+        }
+
+        [Fact]
+        public void AddsScopeToKeyframeNames()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    @keyframes my-animation { /* whatever */ }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    @keyframes my-animation-TestScope { /* whatever */ }
+", result);
+        }
+
+        [Fact]
+        public void RewritesAnimationNamesWhenMatchingKnownKeyframes()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .myclass {
+        color: red;
+        animation: /* ignore comment */ my-animation 1s infinite;
+    }
+
+    .another-thing { animation-name: different-animation; }
+
+    h1 { animation: unknown-animation; } /* Should not be scoped */
+
+    @keyframes my-animation { /* whatever */ }
+    @keyframes different-animation { /* whatever */ }
+    @keyframes unused-animation { /* whatever */ }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .myclass[TestScope] {
+        color: red;
+        animation: /* ignore comment */ my-animation-TestScope 1s infinite;
+    }
+
+    .another-thing[TestScope] { animation-name: different-animation-TestScope; }
+
+    h1[TestScope] { animation: unknown-animation; } /* Should not be scoped */
+
+    @keyframes my-animation-TestScope { /* whatever */ }
+    @keyframes different-animation-TestScope { /* whatever */ }
+    @keyframes unused-animation-TestScope { /* whatever */ }
+", result);
+        }
+
+        [Fact]
+        public void RewritesMultipleAnimationNames()
+        {
+            // Arrange/act
+            var result = RewriteCssCommand.AddScopeToSelectors(@"
+    .myclass1 { animation-name: my-animation , different-animation }
+    .myclass2 { animation: 4s linear 0s alternate my-animation infinite, different-animation 0s }
+    @keyframes my-animation { }
+    @keyframes different-animation { }
+", "TestScope");
+
+            // Assert
+            Assert.Equal(@"
+    .myclass1[TestScope] { animation-name: my-animation-TestScope , different-animation-TestScope }
+    .myclass2[TestScope] { animation: 4s linear 0s alternate my-animation-TestScope infinite, different-animation-TestScope 0s }
+    @keyframes my-animation-TestScope { }
+    @keyframes different-animation-TestScope { }
+", result);
+        }
+    }
+}