diff --git a/bench.rb b/bench.rb
index 75f4908..35333c8 100644
--- a/bench.rb
+++ b/bench.rb
@@ -21,10 +21,13 @@ module ClassVariants
         blue: "text-white bg-blue-500 border-blue-700 hover:bg-blue-600",
         red: "text-white bg-red-500 border-red-700 hover:bg-red-600",
       },
+      block: "justify-center w-full",
+      "!block": "justify-between",
     },
     defaults: {
       size: :base,
       color: :white,
+      block: false,
     }
   )
 
@@ -33,6 +36,6 @@ module ClassVariants
   end
 
   x.report("rendering with overrides") do
-    button_classes.render(size: :sm, color: :red)
+    button_classes.render(size: :sm, color: :red, block: true)
   end
 end
diff --git a/lib/class_variants/instance.rb b/lib/class_variants/instance.rb
index 0c5e1da..c60d25e 100644
--- a/lib/class_variants/instance.rb
+++ b/lib/class_variants/instance.rb
@@ -5,7 +5,7 @@ class ClassVariants::Instance
 
   def initialize(classes = "", variants: {}, defaults: {})
     @classes = classes
-    @variants = variants
+    @variants = expand_boolean_variants(variants)
     @defaults = defaults
   end
 
@@ -26,4 +26,20 @@ def render(**overrides)
     # Return the final token list
     result.join " "
   end
+
+  private
+
+  def expand_boolean_variants(variants)
+    variants.each.map { |key, value|
+      case value
+      when String
+        s_key = key.to_s
+        { s_key.delete_prefix("!").to_sym => { !s_key.start_with?("!") => value } }
+      else
+        { key => value }
+      end
+    }.reduce do |variants, more_variants|
+      variants.merge!(more_variants) { |_key, v1, v2| v1.merge!(v2) }
+    end
+  end
 end
diff --git a/readme.md b/readme.md
index ac6cadd..f2f3ae9 100644
--- a/readme.md
+++ b/readme.md
@@ -52,17 +52,24 @@ button_classes = ClassVariants.build(
       red: "bg-red-600 hover:bg-red-700 focus:ring-red-500",
       blue: "bg-blue-600 hover:bg-blue-700 focus:ring-blue-500",
     },
+    # A variant whose value is a string will be expanded into a hash that looks
+    # like  { true => "classes" }
+    block: "w-full justify-center",
+    # Unless the key starts with !, in which case it will expand into
+    # { false => "classes" }
+    "!block": "w-auto",
   },
   defaults: {
     size: :md,
     color: :indigo,
+    icon: false
   }
 )
 
 # Call it with our desired variants
 button_classes.render(color: :blue, size: :sm)
 button_classes.render
-button_classes.render(color: :red, size: :xl)
+button_classes.render(color: :red, size: :xl, icon: true)
 ```
 
 ## Use with Rails