LibWeb: Prevent max-width expanding the width

Author: https://github.com/emilitzerjo
Commit: bf3144fcff
Pull-request: https://github.com/SerenityOS/serenity/pull/19946
Issue: https://github.com/SerenityOS/serenity/issues/18778
Reviewed-by: https://github.com/awesomekling

Userland/Libraries/LibWeb/Layout/BlockFormattingContext.cpp

@@ -255,7 +255,7 @@ void BlockFormattingContext::compute_width(Box const& box, AvailableSpace const&
     //    but this time using the computed value of 'max-width' as the computed value for 'width'.
     if (!should_treat_max_width_as_none(box, available_space.width)) {
         auto max_width = calculate_inner_width(box, remaining_available_space.width, computed_values.max_width());
-        auto used_width_px = used_width.is_auto() ? remaining_available_space.width.to_px() : used_width.to_px(box);
+        auto used_width_px = used_width.is_auto() ? CSSPixels { 0 } : used_width.to_px(box);
         if (used_width_px > max_width.to_px(box)) {
             used_width = try_compute_width(max_width);
         }