LibWeb: Fill the whole viewport with the correct background color

CSS2 tells us to use the HTML element's background color if not
transparent. Otherwise, the BODY element's background color.

2 files changed, 16 insertions, 13 deletions

diff --git a/Userland/Libraries/LibWeb/DOM/Document.cpp b/Userland/Libraries/LibWeb/DOM/Document.cpp
index 85960232a5..929042dc74 100644
--- a/Userland/Libraries/LibWeb/DOM/Document.cpp
+++ b/Userland/Libraries/LibWeb/DOM/Document.cpp
@@ -489,21 +489,24 @@ void Document::tear_down_layout_tree()
     m_layout_root = nullptr;
 }
 
-Color Document::background_color(const Palette& palette) const
+Color Document::background_color(Gfx::Palette const& palette) const
 {
-    auto default_color = palette.base();
-    auto* body_element = body();
-    if (!body_element)
-        return default_color;
+    // CSS2 says we should use the HTML element's background color unless it's transparent...
+    if (auto* html_element = this->html_element(); html_element && html_element->layout_node()) {
+        auto color = html_element->layout_node()->computed_values().background_color();
+        if (color.alpha())
+            return color;
+    }
 
-    auto* body_layout_node = body_element->layout_node();
-    if (!body_layout_node)
-        return default_color;
+    // ...in which case we use the BODY element's background color.
+    if (auto* body_element = body(); body_element && body_element->layout_node()) {
+        auto color = body_element->layout_node()->computed_values().background_color();
+        if (color.alpha())
+            return color;
+    }
 
-    auto color = body_layout_node->computed_values().background_color();
-    if (!color.alpha())
-        return default_color;
-    return color;
+    // If both HTML and BODY are transparent, we fall back to the system's "base" palette color.
+    return palette.base();
 }
 
 Vector<CSS::BackgroundLayerData> const* Document::background_layers() const
diff --git a/Userland/Libraries/LibWeb/Layout/InitialContainingBlock.cpp b/Userland/Libraries/LibWeb/Layout/InitialContainingBlock.cpp
index a077dfcdcf..8bb8b3582f 100644
--- a/Userland/Libraries/LibWeb/Layout/InitialContainingBlock.cpp
+++ b/Userland/Libraries/LibWeb/Layout/InitialContainingBlock.cpp
@@ -47,7 +47,7 @@ void InitialContainingBlock::build_stacking_context_tree()
 void InitialContainingBlock::paint_all_phases(PaintContext& context)
 {
     build_stacking_context_tree_if_needed();
-    context.painter().fill_rect(enclosing_int_rect(paint_box()->absolute_rect()), context.palette().base());
+    context.painter().fill_rect(enclosing_int_rect(paint_box()->absolute_rect()), document().background_color(context.palette()));
     context.painter().translate(-context.viewport_rect().location());
     paint_box()->stacking_context()->paint(context);
 }