Strip empty props and better empty tags removal

src/CSS.php

@@ -315,6 +315,7 @@ public function execute($path = null, $parents = array())
             $this->extractCustomProperties();
             $css = $this->replace($css);
 
+            $css = $this->stripEmptyProperties($css);
             $css = $this->stripWhitespace($css);
             $css = $this->shortenColors($css);
             $css = $this->shortenZeroes($css);
@@ -621,12 +622,29 @@ protected function shortenZeroes($content)
      */
     protected function stripEmptyTags($content)
     {
+        // Remove empty tags/selectors at the start of the file
         $content = preg_replace('/(?<=^)[^\{\};]+\{\s*\}/', '', $content);
-        $content = preg_replace('/(?<=(\}|;))[^\{\};]+\{\s*\}/', '', $content);
+        // Remove empty tags/selectors (classes, ids and so on)
+        $content = preg_replace('/(?<=(\}|;|\{))[^\{\};]+\{\s*\}/', '', $content);
+        // Run it again to remove any empty media queries that had the empty selectors before
+        $content = preg_replace('/(?<=(\}|;|\{))[^\{\};]+\{\s*\}/', '', $content);
 
         return $content;
     }
 
+    /**
+     * Strip empty properties from source code.
+     * i.e: 'color: ;'
+     *
+     * @param string $content
+     *
+     * @return string
+     */
+    protected function stripEmptyProperties($content)
+    {
+        return preg_replace('/[a-zA-Z-:().#]*:\s*;/', '', $content);
+    }
+
     /**
      * Strip comments from source code.
      */

tests/css/CSSTest.php

@@ -782,6 +782,44 @@ public function dataProvider()
             'ul p{padding-left:calc((var(--icon-size) / 2) + var(--horisontal-space))}',
         );
 
+        $tests[] = array('
+body{
+     background: white;
+}
+
+.classWithEmptyProperties {
+    color::hover: ;
+    font-size: ;
+    font-weight::hover:not(#id.class): ;
+}
+
+@media(max-width: 576px) {
+    .emptyClass {
+    }
+
+    .nonEmptyClass {
+        display: flex;
+        --myColorVar: #fff;
+        color: var(--myColorVar);
+    }
+}
+
+@media(max-width: 850px) {
+    .emptyClassWithEmptyProperties {
+        color: ;
+        --myEmptyColor: ;
+    }
+
+    #emptyId {
+    }
+}
+
+@media(max-width: 1580px) {
+    #emptyId {
+    }
+}
+', 'body{background:#fff}@media(max-width:576px){.nonEmptyClass{display:flex;--myColorVar: #fff;color: var(--myColorVar)}}',
+
         // https://github.com/matthiasmullie/minify/issues/351
         $tests[] = array(
             'clamp(2.5rem, 1rem + 4vw, 4rem)',