Prefer !important rules over non-!important rules in the same ruleset

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ### Unreleased
 
+* Prefer `!important` rules over non-`!important` rules in the same ruleset
 * Minor performance improvements
 
 ### Version v1.21.0

lib/css_parser/rule_set.rb

@@ -89,17 +89,20 @@ def initialize(declarations = {})
       #   puts declarations['margin']
       #   => #<CssParser::RuleSet::Declarations::Value:0x00000000030c1838 @important=true, @order=2, @value="0px auto">
       #
-      # If the property already exists its value will be over-written.
+      # If the property already exists its value will be over-written unless it was !important and the new value
+      # is not !important.
       # If the value is empty - property will be deleted
       def []=(property, value)
         property = normalize_property(property)
+        currently_important = declarations[property]&.important
 
-        if value.is_a?(Value)
+        if value.is_a?(Value) && (!currently_important || value.important)
           declarations[property] = value
         elsif value.to_s.strip.empty?
           delete property
         else
-          declarations[property] = Value.new(value)
+          value = Value.new(value)
+          declarations[property] = value if !currently_important || value.important
         end
       rescue ArgumentError => e
         raise e.exception, "#{property} #{e.message}"

test/test_merging.rb

@@ -109,6 +109,18 @@ def test_merging_important
     assert_equal 'black !important;', merged['color']
   end
 
+  def test_prioritising_important_over_non_important_in_the_same_block
+    rs1 = RuleSet.new(block: 'color: black !important; color: red;')
+    merged = CssParser.merge(rs1)
+    assert_equal 'black !important;', merged['color']
+  end
+
+  def test_prioritising_two_important_declarations_in_the_same_block
+    rs1 = RuleSet.new(block: 'color: black !important; color: red !important;')
+    merged = CssParser.merge(rs1)
+    assert_equal 'red !important;', merged['color']
+  end
+
   def test_merging_multiple_important
     rs1 = RuleSet.new(block: 'color: black !important;', specificity: 1000)
     rs2 = RuleSet.new(block: 'color: red !important;', specificity: 1)