diff --git a/src/components/main/layout/box.rs b/src/components/main/layout/box.rs
index 30f3b452e02..79293d85730 100644
--- a/src/components/main/layout/box.rs
+++ b/src/components/main/layout/box.rs
@@ -85,6 +85,9 @@ pub struct Box {
 
     /// Info specific to the kind of box. Keep this enum small.
     specific: SpecificBoxInfo,
+
+    /// positioned box offsets
+    position_offsets: Slot<SideOffsets2D<Au>>,
 }
 
 /// Info specific to the kind of box. Keep this enum small.
@@ -254,6 +257,7 @@ impl Box {
             padding: Slot::init(Zero::zero()),
             margin: Slot::init(Zero::zero()),
             specific: specific,
+            position_offsets: Slot::init(Zero::zero()),
         }
     }
 
@@ -276,6 +280,7 @@ impl Box {
             padding: Slot::init(self.padding.get()),
             margin: Slot::init(self.margin.get()),
             specific: specific,
+            position_offsets: Slot::init(Zero::zero())
         }
     }
 
@@ -334,6 +339,14 @@ impl Box {
                                                  style.Border.border_left_style)))
     }
 
+    pub fn compute_positioned_offset(&self, style: &ComputedValues) {
+        self.position_offsets.set(SideOffsets2D::new(
+                MaybeAuto::from_style(style.PositionOffsets.top, Au::new(0)).specified_or_zero(),
+                MaybeAuto::from_style(style.PositionOffsets.right, Au::new(0)).specified_or_zero(),
+                MaybeAuto::from_style(style.PositionOffsets.bottom, Au::new(0)).specified_or_zero(),
+                MaybeAuto::from_style(style.PositionOffsets.left, Au::new(0)).specified_or_zero()));
+    }
+
     /// Populates the box model padding parameters from the given computed style.
     pub fn compute_padding(&self, style: &ComputedValues, containing_block_width: Au) {
         let padding = SideOffsets2D::new(self.compute_padding_length(style.Padding.padding_top,
diff --git a/src/components/style/properties.rs.mako b/src/components/style/properties.rs.mako
index 5fefde01f4b..ca0bcac6b0c 100644
--- a/src/components/style/properties.rs.mako
+++ b/src/components/style/properties.rs.mako
@@ -223,6 +223,13 @@ pub mod longhands {
         </%self:longhand>
     % endfor
 
+    ${new_style_struct("PositionOffsets")}
+
+    % for side in ["top", "right", "bottom", "left"]:
+        ${predefined_type(side, "LengthOrPercentageOrAuto",
+                          "computed::LPA_Auto")}
+    % endfor
+
     // CSS 2.1, Section 9 - Visual formatting model
 
     ${new_style_struct("Box")}
@@ -279,6 +286,7 @@ pub mod longhands {
                       "computed::LPN_None",
                       "parse_non_negative")}
 
+
     <%self:single_component_value name="line-height">
         #[deriving(Clone)]
         pub enum SpecifiedValue {