diff --git a/core/fxcrt/css/cfx_cssrulecollection.cpp b/core/fxcrt/css/cfx_cssrulecollection.cpp
index f525821..4b63914 100644
--- a/core/fxcrt/css/cfx_cssrulecollection.cpp
+++ b/core/fxcrt/css/cfx_cssrulecollection.cpp
@@ -34,9 +34,8 @@
 }
 
 void CFX_CSSRuleCollection::AddRulesFrom(const CFX_CSSStyleSheet* sheet) {
-  int32_t iRules = sheet->CountRules();
-  for (int32_t j = 0; j < iRules; j++)
-    AddRulesFrom(sheet, sheet->GetRule(j));
+  for (size_t i = 0; i < sheet->CountRules(); ++i)
+    AddRulesFrom(sheet, sheet->GetRule(i));
 }
 
 void CFX_CSSRuleCollection::AddRulesFrom(const CFX_CSSStyleSheet* pStyleSheet,
diff --git a/core/fxcrt/css/cfx_cssstylesheet.cpp b/core/fxcrt/css/cfx_cssstylesheet.cpp
index df44530..c079097 100644
--- a/core/fxcrt/css/cfx_cssstylesheet.cpp
+++ b/core/fxcrt/css/cfx_cssstylesheet.cpp
@@ -13,7 +13,6 @@
 #include "core/fxcrt/css/cfx_cssstylerule.h"
 #include "core/fxcrt/fx_codepage.h"
 #include "third_party/base/ptr_util.h"
-#include "third_party/base/stl_util.h"
 
 CFX_CSSStyleSheet::CFX_CSSStyleSheet() {}
 
@@ -26,11 +25,11 @@
   m_StringCache.clear();
 }
 
-int32_t CFX_CSSStyleSheet::CountRules() const {
-  return pdfium::CollectionSize<int32_t>(m_RuleArray);
+size_t CFX_CSSStyleSheet::CountRules() const {
+  return m_RuleArray.size();
 }
 
-CFX_CSSStyleRule* CFX_CSSStyleSheet::GetRule(int32_t index) const {
+CFX_CSSStyleRule* CFX_CSSStyleSheet::GetRule(size_t index) const {
   return m_RuleArray[index].get();
 }
 
diff --git a/core/fxcrt/css/cfx_cssstylesheet.h b/core/fxcrt/css/cfx_cssstylesheet.h
index 3f3a94a..ed89106 100644
--- a/core/fxcrt/css/cfx_cssstylesheet.h
+++ b/core/fxcrt/css/cfx_cssstylesheet.h
@@ -23,8 +23,8 @@
 
   bool LoadBuffer(const wchar_t* pBuffer, int32_t iBufSize);
 
-  int32_t CountRules() const;
-  CFX_CSSStyleRule* GetRule(int32_t index) const;
+  size_t CountRules() const;
+  CFX_CSSStyleRule* GetRule(size_t index) const;
 
  private:
   void Reset();
diff --git a/core/fxcrt/css/cfx_cssstylesheet_unittest.cpp b/core/fxcrt/css/cfx_cssstylesheet_unittest.cpp
index 5207ea2..a69c68f 100644
--- a/core/fxcrt/css/cfx_cssstylesheet_unittest.cpp
+++ b/core/fxcrt/css/cfx_cssstylesheet_unittest.cpp
@@ -27,7 +27,7 @@
 
   void TearDown() override { decl_ = nullptr; }
 
-  void LoadAndVerifyRuleCount(const wchar_t* buf, int rule_count) {
+  void LoadAndVerifyRuleCount(const wchar_t* buf, size_t rule_count) {
     ASSERT(sheet_);
     EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
     EXPECT_EQ(sheet_->CountRules(), rule_count);
@@ -100,10 +100,10 @@
   const wchar_t* buf =
       L"a { border: 10px; }\nb { text-decoration: underline; }";
   EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
-  EXPECT_EQ(2, sheet_->CountRules());
+  EXPECT_EQ(2u, sheet_->CountRules());
 
   CFX_CSSStyleRule* style = sheet_->GetRule(0);
-  EXPECT_EQ(1UL, style->CountSelectorLists());
+  EXPECT_EQ(1u, style->CountSelectorLists());
 
   bool found_selector = false;
   uint32_t hash = FX_HashCode_GetW(L"a", true);
@@ -116,7 +116,7 @@
   EXPECT_TRUE(found_selector);
 
   decl_ = style->GetDeclaration();
-  EXPECT_EQ(4UL, decl_->PropertyCountForTesting());
+  EXPECT_EQ(4u, decl_->PropertyCountForTesting());
 
   VerifyFloat(CFX_CSSProperty::BorderLeftWidth, 10.0,
               CFX_CSSNumberType::Pixels);
@@ -127,7 +127,7 @@
               CFX_CSSNumberType::Pixels);
 
   style = sheet_->GetRule(1);
-  EXPECT_EQ(1UL, style->CountSelectorLists());
+  EXPECT_EQ(1u, style->CountSelectorLists());
 
   found_selector = false;
   hash = FX_HashCode_GetW(L"b", true);
@@ -140,7 +140,7 @@
   EXPECT_TRUE(found_selector);
 
   decl_ = style->GetDeclaration();
-  EXPECT_EQ(1UL, decl_->PropertyCountForTesting());
+  EXPECT_EQ(1u, decl_->PropertyCountForTesting());
   VerifyList(CFX_CSSProperty::TextDecoration,
              {CFX_CSSPropertyValue::Underline});
 }
@@ -148,28 +148,28 @@
 TEST_F(CFX_CSSStyleSheetTest, ParseChildSelectors) {
   const wchar_t* buf = L"a b c { border: 10px; }";
   EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
-  EXPECT_EQ(1, sheet_->CountRules());
+  EXPECT_EQ(1u, sheet_->CountRules());
 
   CFX_CSSStyleRule* style = sheet_->GetRule(0);
-  EXPECT_EQ(1UL, style->CountSelectorLists());
+  EXPECT_EQ(1u, style->CountSelectorLists());
 
   auto* sel = style->GetSelectorList(0);
-  EXPECT_TRUE(sel != nullptr);
+  ASSERT_TRUE(sel);
   EXPECT_EQ(FX_HashCode_GetW(L"c", true), sel->GetNameHash());
 
   sel = sel->GetNextSelector();
-  EXPECT_TRUE(sel != nullptr);
+  ASSERT_TRUE(sel);
   EXPECT_EQ(FX_HashCode_GetW(L"b", true), sel->GetNameHash());
 
   sel = sel->GetNextSelector();
-  EXPECT_TRUE(sel != nullptr);
+  ASSERT_TRUE(sel);
   EXPECT_EQ(FX_HashCode_GetW(L"a", true), sel->GetNameHash());
 
   sel = sel->GetNextSelector();
-  EXPECT_TRUE(sel == nullptr);
+  EXPECT_FALSE(sel);
 
   decl_ = style->GetDeclaration();
-  EXPECT_EQ(4UL, decl_->PropertyCountForTesting());
+  EXPECT_EQ(4u, decl_->PropertyCountForTesting());
 
   VerifyFloat(CFX_CSSProperty::BorderLeftWidth, 10.0,
               CFX_CSSNumberType::Pixels);
@@ -183,19 +183,19 @@
 TEST_F(CFX_CSSStyleSheetTest, ParseUnhandledSelectors) {
   const wchar_t* buf = L"a > b { padding: 0; }";
   EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
-  EXPECT_EQ(0, sheet_->CountRules());
+  EXPECT_EQ(0u, sheet_->CountRules());
 
   buf = L"a[first] { padding: 0; }";
   EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
-  EXPECT_EQ(0, sheet_->CountRules());
+  EXPECT_EQ(0u, sheet_->CountRules());
 
   buf = L"a+b { padding: 0; }";
   EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
-  EXPECT_EQ(0, sheet_->CountRules());
+  EXPECT_EQ(0u, sheet_->CountRules());
 
   buf = L"a ^ b { padding: 0; }";
   EXPECT_TRUE(sheet_->LoadBuffer(buf, wcslen(buf)));
-  EXPECT_EQ(0, sheet_->CountRules());
+  EXPECT_EQ(0u, sheet_->CountRules());
 }
 
 TEST_F(CFX_CSSStyleSheetTest, ParseMultipleSelectorsCombined) {