diff --git a/phpstan-baseline.neon b/phpstan-baseline.neon
index b6c9deeb..3927d672 100644
--- a/phpstan-baseline.neon
+++ b/phpstan-baseline.neon
@@ -1110,156 +1110,6 @@ parameters:
 			count: 2
 			path: src/PhpSpreadsheet/DefinedName.php
 
-		-
-			message: "#^Cannot call method setBold\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setColor\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setItalic\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setName\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setSize\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setStrikethrough\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setSubscript\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setSuperscript\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Cannot call method setUnderline\\(\\) on PhpOffice\\\\PhpSpreadsheet\\\\Style\\\\Font\\|null\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:startFontTag\\(\\) has parameter \\$tag with no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$bold has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$color has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$colourMap has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$endTagCallbacks has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$face has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$italic has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$size has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$stack has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$startTagCallbacks has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$strikethrough has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$stringData has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$subscript has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$superscript has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Html\\:\\:\\$underline has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Html.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Sample\\:\\:getSamples\\(\\) should return array\\<array\\<string\\>\\> but returns array\\<string, array\\<string, array\\|string\\>\\>\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Sample.php
-
-		-
-			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Helper\\\\Sample\\:\\:log\\(\\) has parameter \\$message with no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Sample.php
-
-		-
-			message: "#^Parameter \\#1 \\$directory of class RecursiveDirectoryIterator constructor expects string, string\\|false given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Sample.php
-
-		-
-			message: "#^Parameter \\#1 \\$filename of function unlink expects string, string\\|false given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Sample.php
-
-		-
-			message: "#^Parameter \\#1 \\$path of function pathinfo expects string, array\\|string given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Sample.php
-
-		-
-			message: "#^Parameter \\#3 \\$subject of function str_replace expects array\\|string, string\\|false given\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Helper/Sample.php
-
 		-
 			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\IOFactory\\:\\:createReader\\(\\) should return PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\IReader but returns object\\.$#"
 			count: 1
@@ -1619,47 +1469,12 @@ parameters:
 			message: "#^Unreachable statement \\- code above always terminates\\.$#"
 			count: 8
 			path: src/PhpSpreadsheet/Reader/Xls.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\Color\\\\BIFF5\\:\\:\\$map has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\Color\\\\BIFF8\\:\\:\\$map has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\Color\\\\BuiltIn\\:\\:\\$map has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\ErrorCode\\:\\:\\$map has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\RC4\\:\\:\\$i has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/RC4.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\RC4\\:\\:\\$j has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/RC4.php
-
-		-
-			message: "#^Property PhpOffice\\\\PhpSpreadsheet\\\\Reader\\\\Xls\\\\RC4\\:\\:\\$s has no type specified\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Reader/Xls/RC4.php
-
+		
 		-
 			message: "#^Cannot access property \\$r on SimpleXMLElement\\|null\\.$#"
 			count: 2
 			path: src/PhpSpreadsheet/Reader/Xlsx.php
-
+		
 		-
 			message: "#^Parameter \\#1 \\$haystack of function strpos expects string, string\\|false given\\.$#"
 			count: 1
@@ -2145,11 +1960,6 @@ parameters:
 			count: 1
 			path: src/PhpSpreadsheet/Shared/OLERead.php
 
-		-
-			message: "#^Static method PhpOffice\\\\PhpSpreadsheet\\\\Shared\\\\TimeZone\\:\\:validateTimeZone\\(\\) is unused\\.$#"
-			count: 1
-			path: src/PhpSpreadsheet/Shared/TimeZone.php
-
 		-
 			message: "#^Method PhpOffice\\\\PhpSpreadsheet\\\\Shared\\\\Trend\\\\BestFit\\:\\:calculateGoodnessOfFit\\(\\) has parameter \\$const with no type specified\\.$#"
 			count: 1
diff --git a/samples/Calculations/Financial/FV.php b/samples/Calculations/Financial/FV.php
index 31ddb630..40b3366f 100644
--- a/samples/Calculations/Financial/FV.php
+++ b/samples/Calculations/Financial/FV.php
@@ -32,5 +32,5 @@ $worksheet->getStyle('B8:C8')->getNumberFormat()->setFormatCode('$#,##0.00');
 $helper->log($worksheet->getCell('B8')->getValue());
 $helper->log('FV() Result is ' . $worksheet->getCell('B8')->getFormattedValue());
 
-$helper->log($worksheet->getCell('C6')->getValue());
+$helper->log($worksheet->getCell('C8')->getValue());
 $helper->log('FV() Result is ' . $worksheet->getCell('C8')->getFormattedValue());
diff --git a/src/PhpSpreadsheet/Helper/Html.php b/src/PhpSpreadsheet/Helper/Html.php
index 632efebc..b8ed386a 100644
--- a/src/PhpSpreadsheet/Helper/Html.php
+++ b/src/PhpSpreadsheet/Helper/Html.php
@@ -12,7 +12,7 @@ use PhpOffice\PhpSpreadsheet\Style\Font;
 
 class Html
 {
-    protected static $colourMap = [
+    private const COLOUR_MAP = [
         'aliceblue' => 'f0f8ff',
         'antiquewhite' => 'faebd7',
         'antiquewhite1' => 'ffefdb',
@@ -532,25 +532,34 @@ class Html
         'yellowgreen' => '9acd32',
     ];
 
-    protected $face;
+    /** @var ?string */
+    private $face;
 
-    protected $size;
+    /** @var ?string */
+    private $size;
 
-    protected $color;
+    /** @var ?string */
+    private $color;
 
-    protected $bold = false;
+    /** @var bool */
+    private $bold = false;
 
-    protected $italic = false;
+    /** @var bool */
+    private $italic = false;
 
-    protected $underline = false;
+    /** @var bool */
+    private $underline = false;
 
-    protected $superscript = false;
+    /** @var bool */
+    private $superscript = false;
 
-    protected $subscript = false;
+    /** @var bool */
+    private $subscript = false;
 
-    protected $strikethrough = false;
+    /** @var bool */
+    private $strikethrough = false;
 
-    protected $startTagCallbacks = [
+    private const START_TAG_CALLBACKS = [
         'font' => 'startFontTag',
         'b' => 'startBoldTag',
         'strong' => 'startBoldTag',
@@ -563,7 +572,7 @@ class Html
         'sub' => 'startSubscriptTag',
     ];
 
-    protected $endTagCallbacks = [
+    private const END_TAG_CALLBACKS = [
         'font' => 'endFontTag',
         'b' => 'endBoldTag',
         'strong' => 'endBoldTag',
@@ -584,16 +593,18 @@ class Html
         'h6' => 'breakTag',
     ];
 
-    protected $stack = [];
+    /** @var array */
+    private $stack = [];
 
-    protected $stringData = '';
+    /** @var string */
+    private $stringData = '';
 
     /**
      * @var RichText
      */
-    protected $richTextObject;
+    private $richTextObject;
 
-    protected function initialise(): void
+    private function initialise(): void
     {
         $this->face = $this->size = $this->color = null;
         $this->bold = $this->italic = $this->underline = $this->superscript = $this->subscript = $this->strikethrough = false;
@@ -633,7 +644,7 @@ class Html
         return $this->richTextObject;
     }
 
-    protected function cleanWhitespace(): void
+    private function cleanWhitespace(): void
     {
         foreach ($this->richTextObject->getRichTextElements() as $key => $element) {
             $text = $element->getText();
@@ -647,7 +658,7 @@ class Html
         }
     }
 
-    protected function buildTextRun(): void
+    private function buildTextRun(): void
     {
         $text = $this->stringData;
         if (trim($text) === '') {
@@ -655,37 +666,40 @@ class Html
         }
 
         $richtextRun = $this->richTextObject->createTextRun($this->stringData);
-        if ($this->face) {
-            $richtextRun->getFont()->setName($this->face);
-        }
-        if ($this->size) {
-            $richtextRun->getFont()->setSize($this->size);
-        }
-        if ($this->color) {
-            $richtextRun->getFont()->setColor(new Color('ff' . $this->color));
-        }
-        if ($this->bold) {
-            $richtextRun->getFont()->setBold(true);
-        }
-        if ($this->italic) {
-            $richtextRun->getFont()->setItalic(true);
-        }
-        if ($this->underline) {
-            $richtextRun->getFont()->setUnderline(Font::UNDERLINE_SINGLE);
-        }
-        if ($this->superscript) {
-            $richtextRun->getFont()->setSuperscript(true);
-        }
-        if ($this->subscript) {
-            $richtextRun->getFont()->setSubscript(true);
-        }
-        if ($this->strikethrough) {
-            $richtextRun->getFont()->setStrikethrough(true);
+        $font = $richtextRun->getFont();
+        if ($font !== null) {
+            if ($this->face) {
+                $font->setName($this->face);
+            }
+            if ($this->size) {
+                $font->setSize($this->size);
+            }
+            if ($this->color) {
+                $font->setColor(new Color('ff' . $this->color));
+            }
+            if ($this->bold) {
+                $font->setBold(true);
+            }
+            if ($this->italic) {
+                $font->setItalic(true);
+            }
+            if ($this->underline) {
+                $font->setUnderline(Font::UNDERLINE_SINGLE);
+            }
+            if ($this->superscript) {
+                $font->setSuperscript(true);
+            }
+            if ($this->subscript) {
+                $font->setSubscript(true);
+            }
+            if ($this->strikethrough) {
+                $font->setStrikethrough(true);
+            }
         }
         $this->stringData = '';
     }
 
-    protected function rgbToColour(string $rgbValue): string
+    private function rgbToColour(string $rgbValue): string
     {
         preg_match_all('/\d+/', $rgbValue, $values);
         foreach ($values[0] as &$value) {
@@ -697,100 +711,103 @@ class Html
 
     public static function colourNameLookup(string $colorName): string
     {
-        return self::$colourMap[$colorName] ?? '';
+        return self::COLOUR_MAP[$colorName] ?? '';
     }
 
-    protected function startFontTag($tag): void
+    private function startFontTag(DOMElement $tag): void
     {
-        foreach ($tag->attributes as $attribute) {
-            $attributeName = strtolower($attribute->name);
-            $attributeValue = $attribute->value;
+        $attrs = $tag->attributes;
+        if ($attrs !== null) {
+            foreach ($attrs as $attribute) {
+                $attributeName = strtolower($attribute->name);
+                $attributeValue = $attribute->value;
 
-            if ($attributeName == 'color') {
-                if (preg_match('/rgb\s*\(/', $attributeValue)) {
-                    $this->$attributeName = $this->rgbToColour($attributeValue);
-                } elseif (strpos(trim($attributeValue), '#') === 0) {
-                    $this->$attributeName = ltrim($attributeValue, '#');
+                if ($attributeName == 'color') {
+                    if (preg_match('/rgb\s*\(/', $attributeValue)) {
+                        $this->$attributeName = $this->rgbToColour($attributeValue);
+                    } elseif (strpos(trim($attributeValue), '#') === 0) {
+                        $this->$attributeName = ltrim($attributeValue, '#');
+                    } else {
+                        $this->$attributeName = static::colourNameLookup($attributeValue);
+                    }
                 } else {
-                    $this->$attributeName = static::colourNameLookup($attributeValue);
+                    $this->$attributeName = $attributeValue;
                 }
-            } else {
-                $this->$attributeName = $attributeValue;
             }
         }
     }
 
-    protected function endFontTag(): void
+    private function endFontTag(): void
     {
         $this->face = $this->size = $this->color = null;
     }
 
-    protected function startBoldTag(): void
+    private function startBoldTag(): void
     {
         $this->bold = true;
     }
 
-    protected function endBoldTag(): void
+    private function endBoldTag(): void
     {
         $this->bold = false;
     }
 
-    protected function startItalicTag(): void
+    private function startItalicTag(): void
     {
         $this->italic = true;
     }
 
-    protected function endItalicTag(): void
+    private function endItalicTag(): void
     {
         $this->italic = false;
     }
 
-    protected function startUnderlineTag(): void
+    private function startUnderlineTag(): void
     {
         $this->underline = true;
     }
 
-    protected function endUnderlineTag(): void
+    private function endUnderlineTag(): void
     {
         $this->underline = false;
     }
 
-    protected function startSubscriptTag(): void
+    private function startSubscriptTag(): void
     {
         $this->subscript = true;
     }
 
-    protected function endSubscriptTag(): void
+    private function endSubscriptTag(): void
     {
         $this->subscript = false;
     }
 
-    protected function startSuperscriptTag(): void
+    private function startSuperscriptTag(): void
     {
         $this->superscript = true;
     }
 
-    protected function endSuperscriptTag(): void
+    private function endSuperscriptTag(): void
     {
         $this->superscript = false;
     }
 
-    protected function startStrikethruTag(): void
+    private function startStrikethruTag(): void
     {
         $this->strikethrough = true;
     }
 
-    protected function endStrikethruTag(): void
+    private function endStrikethruTag(): void
     {
         $this->strikethrough = false;
     }
 
-    protected function breakTag(): void
+    private function breakTag(): void
     {
         $this->stringData .= "\n";
     }
 
-    protected function parseTextNode(DOMText $textNode): void
+    private function parseTextNode(DOMText $textNode): void
     {
         $domText = (string) preg_replace(
             '/\s+/u',
@@ -804,7 +821,7 @@ class Html
     /**
      * @param string $callbackTag
      */
-    protected function handleCallback(DOMElement $element, $callbackTag, array $callbacks): void
+    private function handleCallback(DOMElement $element, $callbackTag, array $callbacks): void
     {
         if (isset($callbacks[$callbackTag])) {
             $elementHandler = $callbacks[$callbackTag];
@@ -815,20 +832,20 @@ class Html
         }
     }
 
-    protected function parseElementNode(DOMElement $element): void
+    private function parseElementNode(DOMElement $element): void
     {
         $callbackTag = strtolower($element->nodeName);
         $this->stack[] = $callbackTag;
 
-        $this->handleCallback($element, $callbackTag, $this->startTagCallbacks);
+        $this->handleCallback($element, $callbackTag, self::START_TAG_CALLBACKS);
 
         $this->parseElements($element);
         array_pop($this->stack);
 
-        $this->handleCallback($element, $callbackTag, $this->endTagCallbacks);
+        $this->handleCallback($element, $callbackTag, self::END_TAG_CALLBACKS);
     }
 
-    protected function parseElements(DOMNode $element): void
+    private function parseElements(DOMNode $element): void
     {
         foreach ($element->childNodes as $child) {
             if ($child instanceof DOMText) {
diff --git a/src/PhpSpreadsheet/Helper/Sample.php b/src/PhpSpreadsheet/Helper/Sample.php
index 0ac0c796..a0063bd3 100644
--- a/src/PhpSpreadsheet/Helper/Sample.php
+++ b/src/PhpSpreadsheet/Helper/Sample.php
@@ -77,6 +77,11 @@ class Sample
     {
         // Populate samples
         $baseDir = realpath(__DIR__ . '/../../../samples');
+        if ($baseDir === false) {
+            // @codeCoverageIgnoreStart
+            throw new RuntimeException('realpath returned false');
+            // @codeCoverageIgnoreEnd
+        }
         $directory = new RecursiveDirectoryIterator($baseDir);
         $iterator = new RecursiveIteratorIterator($directory);
         $regex = new RegexIterator($iterator, '/^.+\.php$/', RecursiveRegexIterator::GET_MATCH);
@@ -84,6 +89,11 @@ class Sample
         $files = [];
         foreach ($regex as $file) {
             $file = str_replace(str_replace('\\', '/', $baseDir) . '/', '', str_replace('\\', '/', $file[0]));
+            if (is_array($file)) {
+                // @codeCoverageIgnoreStart
+                throw new RuntimeException('str_replace returned array');
+                // @codeCoverageIgnoreEnd
+            }
             $info = pathinfo($file);
             $category = str_replace('_', ' ', $info['dirname'] ?? '');
             $name = str_replace('_', ' ', (string) preg_replace('/(|\.php)/', '', $info['filename']));
@@ -172,12 +182,17 @@ class Sample
     public function getTemporaryFilename($extension = 'xlsx')
     {
         $temporaryFilename = tempnam($this->getTemporaryFolder(), 'phpspreadsheet-');
+        if ($temporaryFilename === false) {
+            // @codeCoverageIgnoreStart
+            throw new RuntimeException('tempnam returned false');
+            // @codeCoverageIgnoreEnd
+        }
         unlink($temporaryFilename);
 
         return $temporaryFilename . '.' . $extension;
     }
 
-    public function log($message): void
+    public function log(string $message): void
     {
         $eol = $this->isCli() ? PHP_EOL : '<br />';
         echo date('H:i:s ') . $message . $eol;
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
index 743d9387..15d0b733 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF5.php
@@ -4,7 +4,7 @@ namespace PhpOffice\PhpSpreadsheet\Reader\Xls\Color;
 
 class BIFF5
 {
-    protected static $map = [
+    private const BIFF5_COLOR_MAP = [
         0x08 => '000000',
         0x09 => 'FFFFFF',
         0x0A => 'FF0000',
@@ -72,10 +72,6 @@ class BIFF5
      */
     public static function lookup($color)
     {
-        if (isset(self::$map[$color])) {
-            return ['rgb' => self::$map[$color]];
-        }
-
-        return ['rgb' => '000000'];
+        return ['rgb' => self::BIFF5_COLOR_MAP[$color] ?? '000000'];
     }
 }
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
index 5c109fb0..019ec79e 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color/BIFF8.php
@@ -4,7 +4,7 @@ namespace PhpOffice\PhpSpreadsheet\Reader\Xls\Color;
 
 class BIFF8
 {
-    protected static $map = [
+    private const BIFF8_COLOR_MAP = [
         0x08 => '000000',
         0x09 => 'FFFFFF',
         0x0A => 'FF0000',
@@ -72,10 +72,6 @@ class BIFF8
      */
     public static function lookup($color)
     {
-        if (isset(self::$map[$color])) {
-            return ['rgb' => self::$map[$color]];
-        }
-
-        return ['rgb' => '000000'];
+        return ['rgb' => self::BIFF8_COLOR_MAP[$color] ?? '000000'];
     }
 }
diff --git a/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php b/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
index 90d50e33..b6a96af8 100644
--- a/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
+++ b/src/PhpSpreadsheet/Reader/Xls/Color/BuiltIn.php
@@ -4,7 +4,7 @@ namespace PhpOffice\PhpSpreadsheet\Reader\Xls\Color;
 
 class BuiltIn
 {
-    protected static $map = [
+    private const BUILTIN_COLOR_MAP = [
         0x00 => '000000',
         0x01 => 'FFFFFF',
         0x02 => 'FF0000',
@@ -26,10 +26,6 @@ class BuiltIn
      */
     public static function lookup($color)
     {
-        if (isset(self::$map[$color])) {
-            return ['rgb' => self::$map[$color]];
-        }
-
-        return ['rgb' => '000000'];
+        return ['rgb' => self::BUILTIN_COLOR_MAP[$color] ?? '000000'];
     }
 }
diff --git a/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php b/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
index 7daf7230..0b79366b 100644
--- a/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
+++ b/src/PhpSpreadsheet/Reader/Xls/ErrorCode.php
@@ -4,7 +4,7 @@ namespace PhpOffice\PhpSpreadsheet\Reader\Xls;
 
 class ErrorCode
 {
-    protected static $map = [
+    private const ERROR_CODE_MAP = [
         0x00 => '#NULL!',
         0x07 => '#DIV/0!',
         0x0F => '#VALUE!',
@@ -23,10 +23,6 @@ class ErrorCode
      */
     public static function lookup($code)
     {
-        if (isset(self::$map[$code])) {
-            return self::$map[$code];
-        }
-
-        return false;
+        return self::ERROR_CODE_MAP[$code] ?? false;
     }
 }
diff --git a/src/PhpSpreadsheet/Reader/Xls/RC4.php b/src/PhpSpreadsheet/Reader/Xls/RC4.php
index 691aca7c..b7c7c900 100644
--- a/src/PhpSpreadsheet/Reader/Xls/RC4.php
+++ b/src/PhpSpreadsheet/Reader/Xls/RC4.php
@@ -4,11 +4,13 @@ namespace PhpOffice\PhpSpreadsheet\Reader\Xls;
 
 class RC4
 {
-    // Context
-    protected $s = [];
+    /** @var int[] */
+    protected $s = []; // Context
 
+    /** @var int */
     protected $i = 0;
 
+    /** @var int */
     protected $j = 0;
 
     /**
diff --git a/src/PhpSpreadsheet/Shared/TimeZone.php b/src/PhpSpreadsheet/Shared/TimeZone.php
index 734c076d..324e3424 100644
--- a/src/PhpSpreadsheet/Shared/TimeZone.php
+++ b/src/PhpSpreadsheet/Shared/TimeZone.php
@@ -35,7 +35,7 @@ class TimeZone
      */
     public static function setTimeZone(string $timezoneName): bool
     {
-        if (self::validateTimezone($timezoneName)) {
+        if (self::validateTimeZone($timezoneName)) {
             self::$timezone = $timezoneName;
 
             return true;
@@ -67,7 +67,7 @@ class TimeZone
     {
         $timezoneName = $timezoneName ?? self::$timezone;
         $dtobj = Date::dateTimeFromTimestamp("$timestamp");
-        if (!self::validateTimezone($timezoneName)) {
+        if (!self::validateTimeZone($timezoneName)) {
             throw new PhpSpreadsheetException("Invalid timezone $timezoneName");
         }
         $dtobj->setTimeZone(new DateTimeZone($timezoneName));
diff --git a/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php b/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php
index cabac403..ad395ace 100644
--- a/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php
+++ b/tests/PhpSpreadsheetTests/Reader/Html/HtmlTest.php
@@ -80,6 +80,7 @@ class HtmlTest extends TestCase
                     <tr>
                         <td style="background-color: #0000FF;color: #FFFFFF">Blue background</td>
                         <td style="background-color: unknown1;color: unknown2">Unknown fore/background</td>
+                        <td style="background-color: antiquewhite2;color: aliceblue">Unknown fore/background</td>
                     </tr>
                 </table>';
         $filename = HtmlHelper::createHtml($html);
@@ -93,6 +94,10 @@ class HtmlTest extends TestCase
         self::assertEquals('000000', $style->getFont()->getColor()->getRGB());
         self::assertEquals('000000', $style->getFill()->getEndColor()->getRGB());
         self::assertEquals('FFFFFF', $style->getFill()->getstartColor()->getRGB());
+        $style = $firstSheet->getCell('C1')->getStyle();
+        self::assertEquals('f0f8ff', $style->getFont()->getColor()->getRGB());
+        self::assertEquals('eedfcc', $style->getFill()->getEndColor()->getRGB());
+        self::assertEquals('eedfcc', $style->getFill()->getstartColor()->getRGB());
     }
 
     public function testCanApplyInlineFontStyles(): void
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php
new file mode 100644
index 00000000..977b852b
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ColorMapTest.php
@@ -0,0 +1,34 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xls\Color\BIFF5;
+use PhpOffice\PhpSpreadsheet\Reader\Xls\Color\BIFF8;
+use PhpOffice\PhpSpreadsheet\Reader\Xls\Color\BuiltIn;
+use PHPUnit\Framework\TestCase;
+
+class ColorMapTest extends TestCase
+{
+    /**
+     * @dataProvider colorMapProvider
+     */
+    public function testColorMap(int $index, string $expectedBiff5, string $expectedBiff8, string $expectedBuiltin): void
+    {
+        self::assertSame($expectedBiff5, BIFF5::lookup($index)['rgb']);
+        self::assertSame($expectedBiff8, BIFF8::lookup($index)['rgb']);
+        self::assertSame($expectedBuiltin, BuiltIn::lookup($index)['rgb']);
+    }
+
+    public function colorMapProvider(): array
+    {
+        return [
+            'default builtin' => [0x00, '000000', '000000', '000000'],
+            'non-default builtin' => [0x02, '000000', '000000', 'FF0000'],
+            'system window text color' => [0x40, '000000', '000000', '000000'],
+            'system window background color' => [0x41, '000000', '000000', 'FFFFFF'],
+            'same biff5/8' => [0x09, 'FFFFFF', 'FFFFFF', '000000'],
+            'different biff5/8' => [0x29, '69FFFF', 'CCFFFF', '000000'],
+
+        ];
+    }
+}
diff --git a/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php b/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php
new file mode 100644
index 00000000..e857d84f
--- /dev/null
+++ b/tests/PhpSpreadsheetTests/Reader/Xls/ErrorCodeMapTest.php
@@ -0,0 +1,33 @@
+<?php
+
+namespace PhpOffice\PhpSpreadsheetTests\Reader\Xls;
+
+use PhpOffice\PhpSpreadsheet\Reader\Xls\ErrorCode;
+use PHPUnit\Framework\TestCase;
+
+class ErrorCodeMapTest extends TestCase
+{
+    /**
+     * @param bool|string $expected
+     *
+     * @dataProvider errorCodeMapProvider
+     */
+    public function testErrorCode($expected, int $index): void
+    {
+        self::assertSame($expected, ErrorCode::lookup($index));
+    }
+
+    public function errorCodeMapProvider(): array
+    {
+        return [
+            [false, 0x01],
+            ['#NULL!', 0x00],
+            ['#DIV/0!', 0x07],
+            ['#VALUE!', 0x0F],
+            ['#REF!', 0x17],
+            ['#NAME?', 0x1d],
+            ['#NUM!', 0x24],
+            ['#N/A', 0x2a],
+        ];
+    }
+}