Border Tweak

Do not override base style if conditional style indicates BORDER_OMIT.

Do not export BORDER_NONE color 0 for conditional; same approach is already taken for unconditional.

src/PhpSpreadsheet/Style/ConditionalFormatting/StyleMerger.php

@@ -78,7 +78,11 @@ class StyleMerger
 
     protected function mergeBorderStyle(Border $baseBorderStyle, Border $borderStyle): void
     {
-        $baseBorderStyle->setBorderStyle($borderStyle->getBorderStyle());
+        if ($borderStyle->getBorderStyle() !== Border::BORDER_OMIT) {
+            $baseBorderStyle->setBorderStyle(
+                $borderStyle->getBorderStyle()
+            );
+        }
         if ($borderStyle->getColor()->getARGB() !== null) {
             $baseBorderStyle->setColor($borderStyle->getColor());
         }

src/PhpSpreadsheet/Writer/Html.php

@@ -1658,7 +1658,9 @@ class Html extends BaseWriter
                     $holdCss = '';
                 }
                 foreach ($styles as $key => $value) {
-                    $html .= $key . ':' . $value . ';';
+                    if (!str_starts_with($key, 'border-') || $value !== 'none #000000') {
+                        $html .= $key . ':' . $value . ';';
+                    }
                 }
                 $html .= '"';
             }