diff -r 7b1b88e27a20 -r 48c4eec2b7e6 wp/wp-includes/block-supports/background.php
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/wp/wp-includes/block-supports/background.php	Fri Sep 05 18:40:08 2025 +0200
@@ -0,0 +1,115 @@
+<?php
+/**
+ * Background block support flag.
+ *
+ * @package WordPress
+ * @since 6.4.0
+ */
+
+/**
+ * Registers the style block attribute for block types that support it.
+ *
+ * @since 6.4.0
+ * @access private
+ *
+ * @param WP_Block_Type $block_type Block Type.
+ */
+function wp_register_background_support( $block_type ) {
+	// Setup attributes and styles within that if needed.
+	if ( ! $block_type->attributes ) {
+		$block_type->attributes = array();
+	}
+
+	// Check for existing style attribute definition e.g. from block.json.
+	if ( array_key_exists( 'style', $block_type->attributes ) ) {
+		return;
+	}
+
+	$has_background_support = block_has_support( $block_type, array( 'background' ), false );
+
+	if ( $has_background_support ) {
+		$block_type->attributes['style'] = array(
+			'type' => 'object',
+		);
+	}
+}
+
+/**
+ * Renders the background styles to the block wrapper.
+ * This block support uses the `render_block` hook to ensure that
+ * it is also applied to non-server-rendered blocks.
+ *
+ * @since 6.4.0
+ * @since 6.5.0 Added support for `backgroundPosition` and `backgroundRepeat` output.
+ * @since 6.6.0 Removed requirement for `backgroundImage.source`. A file/url is the default.
+ *
+ * @access private
+ *
+ * @param  string $block_content Rendered block content.
+ * @param  array  $block         Block object.
+ * @return string Filtered block content.
+ */
+function wp_render_background_support( $block_content, $block ) {
+	$block_type                   = WP_Block_Type_Registry::get_instance()->get_registered( $block['blockName'] );
+	$block_attributes             = ( isset( $block['attrs'] ) && is_array( $block['attrs'] ) ) ? $block['attrs'] : array();
+	$has_background_image_support = block_has_support( $block_type, array( 'background', 'backgroundImage' ), false );
+
+	if (
+		! $has_background_image_support ||
+		wp_should_skip_block_supports_serialization( $block_type, 'background', 'backgroundImage' ) ||
+		! isset( $block_attributes['style']['background'] )
+	) {
+		return $block_content;
+	}
+
+	$background_styles                    = array();
+	$background_styles['backgroundImage'] = isset( $block_attributes['style']['background']['backgroundImage'] ) ? $block_attributes['style']['background']['backgroundImage'] : array();
+
+	if ( ! empty( $background_styles['backgroundImage'] ) ) {
+		$background_styles['backgroundSize']     = isset( $block_attributes['style']['background']['backgroundSize'] ) ? $block_attributes['style']['background']['backgroundSize'] : 'cover';
+		$background_styles['backgroundPosition'] = isset( $block_attributes['style']['background']['backgroundPosition'] ) ? $block_attributes['style']['background']['backgroundPosition'] : null;
+		$background_styles['backgroundRepeat']   = isset( $block_attributes['style']['background']['backgroundRepeat'] ) ? $block_attributes['style']['background']['backgroundRepeat'] : null;
+
+		// If the background size is set to `contain` and no position is set, set the position to `center`.
+		if ( 'contain' === $background_styles['backgroundSize'] && ! $background_styles['backgroundPosition'] ) {
+			$background_styles['backgroundPosition'] = 'center';
+		}
+	}
+
+	$styles = wp_style_engine_get_styles( array( 'background' => $background_styles ) );
+
+	if ( ! empty( $styles['css'] ) ) {
+		// Inject background styles to the first element, presuming it's the wrapper, if it exists.
+		$tags = new WP_HTML_Tag_Processor( $block_content );
+
+		if ( $tags->next_tag() ) {
+			$existing_style = $tags->get_attribute( 'style' );
+			$updated_style  = '';
+
+			if ( ! empty( $existing_style ) ) {
+				$updated_style = $existing_style;
+				if ( ! str_ends_with( $existing_style, ';' ) ) {
+					$updated_style .= ';';
+				}
+			}
+
+			$updated_style .= $styles['css'];
+			$tags->set_attribute( 'style', $updated_style );
+			$tags->add_class( 'has-background' );
+		}
+
+		return $tags->get_updated_html();
+	}
+
+	return $block_content;
+}
+
+// Register the block support.
+WP_Block_Supports::get_instance()->register(
+	'background',
+	array(
+		'register_attribute' => 'wp_register_background_support',
+	)
+);
+
+add_filter( 'render_block', 'wp_render_background_support', 10, 2 );