diff --git a/core/fxcrt/BUILD.gn b/core/fxcrt/BUILD.gn
index 1512f97..9a2c710 100644
--- a/core/fxcrt/BUILD.gn
+++ b/core/fxcrt/BUILD.gn
@@ -174,6 +174,7 @@
       "cfx_memorystream_unittest.cpp",
       "css/cfx_cssdeclaration_unittest.cpp",
       "css/cfx_cssstylesheet_unittest.cpp",
+      "css/cfx_csssyntaxparser_unittest.cpp",
       "css/cfx_cssvaluelistparser_unittest.cpp",
     ]
     deps += [
diff --git a/core/fxcrt/css/cfx_csssyntaxparser_unittest.cpp b/core/fxcrt/css/cfx_csssyntaxparser_unittest.cpp
new file mode 100644
index 0000000..4eb0c7a
--- /dev/null
+++ b/core/fxcrt/css/cfx_csssyntaxparser_unittest.cpp
@@ -0,0 +1,212 @@
+// Copyright 2020 PDFium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "core/fxcrt/css/cfx_csssyntaxparser.h"
+
+#include "testing/gtest/include/gtest/gtest.h"
+
+// These tests cover the "declaration only" mode of the CSS Syntax Parser
+// (i.e. inline style="" attribute). The cfx_cssstylesheet_unitttest.cpp
+// file covers the full-up selector { ... } parsing.
+
+TEST(CSSSyntaxParserTest, ParseEmpty) {
+  const wchar_t* input = L"";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseBlank) {
+  const wchar_t* input = L"  \n\r\t";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseMissingColon) {
+  const wchar_t* input = L"foo ";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseMissingValue) {
+  const wchar_t* input = L"foo: ";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseSingleProp1) {
+  const wchar_t* input = L"foo:bar";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseSingleProp2) {
+  const wchar_t* input = L"foo:bar;";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseMissingColonMultiple) {
+  const wchar_t* input = L"foo:bar; baz";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseMissingPropertyMultiple) {
+  const wchar_t* input = L"foo:bar; baz: ";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"baz", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseMultipleProp1) {
+  const wchar_t* input = L"foo : bar; baz : bam";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"baz", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bam", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseMultipleProp2) {
+  const wchar_t* input = L"foo:bar;baz:bam;";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"baz", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bam", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kEOS, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseOpenBrace1) {
+  const wchar_t* input = L"{a:3}";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+
+  // TODO(tsepez): these should fail on stray punctuation.
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"{a", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"3", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseOpenBrace2) {
+  const wchar_t* input = L"foo {a:3}";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+
+  // TODO(tsepez): these should fail on stray punctuation.
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo {a", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"3", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseOpenBrace3) {
+  const wchar_t* input = L"foo: bar {a:3}";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+
+  // TODO(tsepez): these should fail on stray punctuation.
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar {a:3", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseOpenBrace4) {
+  const wchar_t* input = L"foo: bar; {a:3}";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+
+  // TODO(tsepez): these should fail on stray punctuation.
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"{a", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"3", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseCloseBrace1) {
+  const wchar_t* input = L"} foo:bar";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseCloseBrace2) {
+  const wchar_t* input = L"foo}:bar";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseCloseBrace3) {
+  const wchar_t* input = L"foo:bar}";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}
+
+TEST(CSSSyntaxParserTest, ParseCloseBrace4) {
+  const wchar_t* input = L"foo:bar;}";
+  CFX_CSSSyntaxParser parser(input, wcslen(input));
+  parser.SetParseOnlyDeclarations();
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyName, parser.DoSyntaxParse());
+  EXPECT_EQ(L"foo", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kPropertyValue, parser.DoSyntaxParse());
+  EXPECT_EQ(L"bar", parser.GetCurrentString());
+  EXPECT_EQ(CFX_CSSSyntaxStatus::kError, parser.DoSyntaxParse());
+}