LibWeb: Account for negative margins when calculating float intrusion

If a box has a negative margin-left, it may have a negative effective
offset within its parent BFC root coordinate system.

We can account for this when calculating the amount of left-side float
intrusion by flooring the X offset at 0.

2 files changed, 2 insertions, 2 deletions

diff --git a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
index 17961989c1..e362008da1 100644
--- a/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
+++ b/Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp
@@ -1066,7 +1066,7 @@ FormattingContext::SpaceUsedByFloats BlockFormattingContext::intrusion_by_floats
     CSSPixels y_in_root = box_in_root_rect.y() + y_in_box;
     auto space_used_by_floats_in_root = space_used_by_floats(y_in_root);
 
-    auto left_intrusion = max(CSSPixels(0), space_used_by_floats_in_root.left - box_in_root_rect.x());
+    auto left_intrusion = max(CSSPixels(0), space_used_by_floats_in_root.left - max(CSSPixels(0), box_in_root_rect.x()));
 
     CSSPixels offset_from_containing_block_chain_margins_between_here_and_root = 0;
     for (auto const* containing_block = static_cast<Box const*>(&box); containing_block && containing_block != &root(); containing_block = containing_block->containing_block()) {
diff --git a/Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp b/Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp
index 5284d433c0..3dd30d58f6 100644
--- a/Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp
+++ b/Userland/Libraries/LibWeb/Layout/InlineFormattingContext.cpp
@@ -51,7 +51,7 @@ CSSPixels InlineFormattingContext::leftmost_x_offset_at(CSSPixels y) const
     }
     // The left edge of the containing block is to the left of the rightmost left-side float.
     // We adjust the inline content insertion point by the overlap between the containing block and the float.
-    return space.left - box_in_root_rect.x();
+    return space.left - max(CSSPixels(0), box_in_root_rect.x());
 }
 
 CSSPixels InlineFormattingContext::available_space_for_line(CSSPixels y) const