diff --git a/clay.cabal b/clay.cabal
--- a/clay.cabal
+++ b/clay.cabal
@@ -1,5 +1,5 @@
 Name:     clay
-Version:  0.13.0
+Version:  0.13.1
 Synopsis: CSS preprocessor as embedded Haskell.
 Description:
   Clay is a CSS preprocessor like LESS and Sass, but implemented as an embedded
@@ -24,9 +24,10 @@
 Build-Type:    Simple
 
 Tested-With:
-  GHC==7.8.4,
   GHC==7.10.3,
-  GHC==8.0.1
+  GHC==8.0.2,
+  GHC==8.2.2,
+  GHC==8.4.1
 
 Source-Repository head
   Type:     git
@@ -70,19 +71,28 @@
 
   GHC-Options: -Wall
   Build-Depends:
-    base  >= 4.5  && < 5,
+    base  >= 4.7  && < 5,
     mtl   >= 1    && < 2.3,
     text  >= 0.11 && < 1.3
+  if impl(ghc < 8.0)
+    Build-Depends:
+      semigroups
+  else
+    GHC-Options: -Wcompat
 
 Test-Suite Test-Clay
   Type: exitcode-stdio-1.0
   HS-Source-Dirs: spec, src
   main-is: Spec.hs
   Build-Depends:
-    base                 >= 4.5  && < 5,
-    base                 >= 4     && < 5,
+    base                 >= 4.7  && < 5,
     mtl                  >= 1     && < 2.3,
     text                 >= 0.11  && < 1.3,
-    hspec-expectations   >= 0.7.2 && < 0.9,
-    hspec                >= 2.2.0 && < 2.5
+    hspec                >= 2.2.0 && < 2.6,
+    hspec-discover       >= 2.2.0 && < 2.6
+  if impl(ghc < 8.0)
+    Build-Depends:
+      semigroups
+  else
+    GHC-Options: -Wcompat
   Ghc-Options: -Wall
diff --git a/src/Clay/Color.hs b/src/Clay/Color.hs
--- a/src/Clay/Color.hs
+++ b/src/Clay/Color.hs
@@ -4,9 +4,9 @@
 import Data.Char (isHexDigit)
 import Data.Monoid
 import Data.String
-import Data.Text (Text)
 import Text.Printf
 
+import Data.Text (Text)
 import qualified Data.Text as Text
 import Data.Text.Read as Text
 
diff --git a/src/Clay/Comments.hs b/src/Clay/Comments.hs
--- a/src/Clay/Comments.hs
+++ b/src/Clay/Comments.hs
@@ -1,8 +1,10 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE ViewPatterns #-}
 {-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE OverloadedStrings #-}
 module Clay.Comments where
 
+import Data.Foldable (foldMap)
 import Data.Monoid ((<>))
 import Data.Maybe (isNothing)
 import Data.List (partition)
@@ -26,5 +28,7 @@
 addComment c (Property ms k v  ) = Property (Comment c : ms) k v
 addComment _ r                   = r
 
+#if __GLASGOW_HASKELL__ >= 710
 pattern PartitionComments :: [Modifier] -> Maybe CommentText -> [Modifier]
+#endif
 pattern PartitionComments xs cs <- (fmap (foldMap _Comment) . partition (isNothing . _Comment) -> (xs, cs))
diff --git a/src/Clay/Display.hs b/src/Clay/Display.hs
--- a/src/Clay/Display.hs
+++ b/src/Clay/Display.hs
@@ -17,7 +17,7 @@
 
 , Position
 , position
-, static, absolute, fixed, relative
+, static, absolute, fixed, relative, sticky
 
 -- * Display
 
@@ -82,7 +82,7 @@
 import Clay.Property
 import Clay.Stylesheet
 import Clay.Common
-import Data.Text (Text)    
+import Data.Text (Text)
 
 -------------------------------------------------------------------------------
 
@@ -116,12 +116,13 @@
 newtype Position = Position Value
   deriving (Val, Other, Inherit)
 
-static, absolute, fixed, relative :: Position
+static, absolute, fixed, relative, sticky :: Position
 
 static   = Position "static"
 absolute = Position "absolute"
 fixed    = Position "fixed"
 relative = Position "relative"
+sticky = Position "sticky"
 
 position :: Position -> Css
 position = key "position"
@@ -239,7 +240,7 @@
 instance VerticalAlign VerticalAlignValue
 instance VerticalAlign (Size a)
 
-middle,vAlignSub,vAlignSuper,textTop,textBottom,vAlignTop,vAlignBottom,vAlignBaseline :: VerticalAlignValue 
+middle,vAlignSub,vAlignSuper,textTop,textBottom,vAlignTop,vAlignBottom,vAlignBaseline :: VerticalAlignValue
 
 middle = VerticalAlignValue "middle"
 vAlignSub = VerticalAlignValue "sub"
@@ -250,7 +251,7 @@
 vAlignTop = VerticalAlignValue "top"
 vAlignBottom = VerticalAlignValue "bottom"
 
--------------------------------------------------------------------------------               
+-------------------------------------------------------------------------------
 
 class (Val a) => Cursor a where
     cursor :: a -> Css
@@ -261,7 +262,7 @@
 instance Cursor (CursorValue a)
 
 crosshair,cursorDefault,pointer,move,eResize,neResize,nwResize,nResize,seResize,swResize,sResize,wResize,cursorText,wait,cursorProgress,help :: CursorValue Value
-                                                                                                                                          
+
 crosshair = CursorValue "crosshair"
 cursorDefault = CursorValue "default"
 pointer = CursorValue "pointer"
diff --git a/src/Clay/List.hs b/src/Clay/List.hs
--- a/src/Clay/List.hs
+++ b/src/Clay/List.hs
@@ -36,7 +36,7 @@
 )
 where
 
-import Data.Monoid
+import Data.Semigroup
 import Data.Text (Text)
 
 import Clay.Common
diff --git a/src/Clay/Mask.hs b/src/Clay/Mask.hs
--- a/src/Clay/Mask.hs
+++ b/src/Clay/Mask.hs
@@ -57,7 +57,7 @@
 )
 where
 
-import Data.Monoid
+import Data.Semigroup
 
 import Clay.Background
 import Clay.Common
diff --git a/src/Clay/Property.hs b/src/Clay/Property.hs
--- a/src/Clay/Property.hs
+++ b/src/Clay/Property.hs
@@ -2,11 +2,11 @@
 module Clay.Property where
 
 import Control.Arrow (second)
-import Control.Monad.Writer
 import Data.Fixed (Fixed, HasResolution (resolution), showFixed)
 import Data.List (partition, sort)
 import Data.List.NonEmpty (NonEmpty, toList)
 import Data.Maybe
+import Data.Semigroup
 import Data.String
 import Data.Text (Text, replace)
 
@@ -16,9 +16,12 @@
 instance IsString Prefixed where
   fromString s = Plain (fromString s)
 
+instance Semigroup Prefixed where
+  (<>) = merge
+
 instance Monoid Prefixed where
   mempty  = ""
-  mappend = merge
+  mappend = (<>)
 
 merge :: Prefixed -> Prefixed -> Prefixed
 merge (Plain    x ) (Plain    y ) = Plain (x <> y)
@@ -41,7 +44,7 @@
 -------------------------------------------------------------------------------
 
 newtype Key a = Key { unKeys :: Prefixed }
-  deriving (Show, Monoid, IsString)
+  deriving (Show, Semigroup, Monoid, IsString)
 
 cast :: Key a -> Key ()
 cast (Key k) = Key k
@@ -49,7 +52,7 @@
 -------------------------------------------------------------------------------
 
 newtype Value = Value { unValue :: Prefixed }
-  deriving (Show, Monoid, IsString, Eq)
+  deriving (Show, Semigroup, Monoid, IsString, Eq)
 
 class Val a where
   value :: a -> Value
@@ -58,7 +61,7 @@
   value t = Value (Plain t)
 
 newtype Literal = Literal Text
-  deriving (Show, Monoid, IsString)
+  deriving (Show, Semigroup, Monoid, IsString)
 
 instance Val Literal where
   value (Literal t) = Value (Plain (quote t))
@@ -100,7 +103,7 @@
 
 intercalate :: Monoid a => a -> [a] -> a
 intercalate _ []     = mempty
-intercalate s (x:xs) = foldl (\a b -> a <> s <> b) x xs
+intercalate s (x:xs) = foldl (\a b -> a `mappend` s `mappend` b) x xs
 
 -------------------------------------------------------------------------------
 
diff --git a/src/Clay/Selector.hs b/src/Clay/Selector.hs
--- a/src/Clay/Selector.hs
+++ b/src/Clay/Selector.hs
@@ -11,15 +11,10 @@
 module Clay.Selector where
 
 import Control.Applicative
-import Data.Monoid
+import Data.Semigroup
 import Data.String
 import Data.Text (Text)
-import Prelude hiding (foldl)
 
-#if MIN_VERSION_base(4,9,0)
-import Data.Semigroup
-#endif
-
 import qualified Data.Text as Text
 
 -- | The star selector applies to all elements. Maps to @*@ in CSS.
@@ -157,7 +152,7 @@
   deriving (Eq, Ord, Show)
 
 newtype Refinement = Refinement { unFilter :: [Predicate] }
-  deriving (Show, Monoid)
+  deriving (Show, Semigroup, Monoid)
 
 instance IsString Refinement where
   fromString = refinementFromText . fromString
@@ -204,12 +199,9 @@
       -> with star (refinementFromText t)
     _ -> In $ SelectorF (Refinement []) (Elem t)
 
-#if MIN_VERSION_base(4,9,0)
 instance Semigroup (Fix SelectorF) where
-  (<>) = mappend
-#endif
+  a <> b = In (SelectorF (Refinement []) (Combined a b))
 
 instance Monoid (Fix SelectorF) where
-  mempty      = error "Selector is a semigroup"
-  mappend a b = In (SelectorF (Refinement []) (Combined a b))
-
+  mempty  = error "Selector is a semigroup"
+  mappend = (<>)
diff --git a/src/Clay/Stylesheet.hs b/src/Clay/Stylesheet.hs
--- a/src/Clay/Stylesheet.hs
+++ b/src/Clay/Stylesheet.hs
@@ -6,9 +6,11 @@
 
 import Control.Applicative
 import Control.Arrow (second)
-import Control.Monad.Writer hiding (All)
+import Control.Monad.Writer (Writer, execWriter, tell)
+import Data.Foldable (foldMap)
 import Data.Maybe (isJust)
-import Data.Semigroup (Semigroup)
+import Data.Monoid (Monoid(..))
+import Data.Semigroup (Semigroup(..))
 import Data.String (IsString)
 import Data.Text (Text)
 
@@ -83,9 +85,12 @@
 
 type Css = StyleM ()
 
+instance Semigroup Css where
+  (<>) = liftA2 (<>)
+
 instance Monoid Css where
   mempty = pure ()
-  mappend = liftA2 mappend
+  mappend = (<>)
 
 -- | Add a new style property to the stylesheet with the specified `Key` and
 -- value. The value can be any type that is in the `Val' typeclass, with other
diff --git a/src/Clay/Transition.hs b/src/Clay/Transition.hs
--- a/src/Clay/Transition.hs
+++ b/src/Clay/Transition.hs
@@ -83,7 +83,10 @@
 easeInOut  = other "ease-in-out"
 linear     = other "linear"
 stepStart  = other "step-start"
-stepStop   = other "step-stop"
+stepEnd    = other "step-end"
+
+stepStop   = stepEnd
+{-# DEPRECATED stepStop "Use `stepEnd` instead." #-}
 
 stepsStart, stepsStop :: Integer -> TimingFunction