LibWeb: Stop allowing position:relative to affect layout

Relatively positioned boxes should not affect the *layout* of their
siblings. So instead of applying relative inset as a layout-time
translation on the box, we now perform the adjustment at the paintable
level instead.

This makes position:relative actually work as expected, and exposes some
new bugs we need to take care of for Acid2. :^)

1 files changed, 9 insertions, 2 deletions

diff --git a/Userland/Libraries/LibWeb/Painting/PaintableBox.cpp b/Userland/Libraries/LibWeb/Painting/PaintableBox.cpp
index 1f533ed309..007d884869 100644
--- a/Userland/Libraries/LibWeb/Painting/PaintableBox.cpp
+++ b/Userland/Libraries/LibWeb/Painting/PaintableBox.cpp
@@ -59,11 +59,18 @@ void PaintableBox::set_content_size(Gfx::FloatSize const& size)
 
 Gfx::FloatPoint PaintableBox::effective_offset() const
 {
+    Gfx::FloatPoint offset;
     if (m_containing_line_box_fragment.has_value()) {
         auto const& fragment = containing_block()->paint_box()->line_boxes()[m_containing_line_box_fragment->line_box_index].fragments()[m_containing_line_box_fragment->fragment_index];
-        return fragment.offset();
+        offset = fragment.offset();
+    } else {
+        offset = m_offset;
+    }
+    if (layout_box().computed_values().position() == CSS::Position::Relative) {
+        auto const& inset = layout_box().box_model().inset;
+        offset.translate_by(inset.left, inset.top);
     }
-    return m_offset;
+    return offset;
 }
 
 Gfx::FloatRect PaintableBox::compute_absolute_rect() const