diff --git a/src/wp-includes/block-supports/custom-css.php b/src/wp-includes/block-supports/custom-css.php
index 7865b7342639e..391cd45589bb5 100644
--- a/src/wp-includes/block-supports/custom-css.php
+++ b/src/wp-includes/block-supports/custom-css.php
@@ -73,10 +73,21 @@ function wp_render_custom_css_support_styles( $parsed_block ) {
 		 * {@see wp_unique_id_from_values()}. Explicitly declare the `wp-block-library`
 		 * dependency so `global-styles` is guaranteed to print after it, preventing
 		 * block default styles from unintentionally overriding global styles.
+		 *
+		 * Also depend on `block-style-variation-styles` so custom CSS always prints
+		 * after block style variation styles and wins the cascade at equal
+		 * specificity; without an explicit dependency the order is decided by
+		 * enqueue order. The handle must be registered here if it doesn't exist
+		 * yet (it is normally registered lazily while rendering a block with a
+		 * variation), because a style with an unregistered dependency is never
+		 * printed.
 		 */
 		$handle = 'wp-block-custom-css';
 		if ( ! wp_style_is( $handle, 'registered' ) ) {
-			wp_register_style( $handle, false, array( 'wp-block-library', 'global-styles' ) );
+			if ( ! wp_style_is( 'block-style-variation-styles', 'registered' ) ) {
+				wp_register_style( 'block-style-variation-styles', false, array( 'wp-block-library', 'global-styles' ) );
+			}
+			wp_register_style( $handle, false, array( 'wp-block-library', 'global-styles', 'block-style-variation-styles' ) );
 		}
 		$after_styles = wp_styles()->get_data( $handle, 'after' );
 		if ( ! is_array( $after_styles ) ) {
diff --git a/tests/phpunit/tests/block-supports/wpRenderCustomCssSupportStyles.php b/tests/phpunit/tests/block-supports/wpRenderCustomCssSupportStyles.php
index e9556254311b8..65a30aa539947 100644
--- a/tests/phpunit/tests/block-supports/wpRenderCustomCssSupportStyles.php
+++ b/tests/phpunit/tests/block-supports/wpRenderCustomCssSupportStyles.php
@@ -11,12 +11,22 @@ class Tests_Block_Supports_WpRenderCustomCssSupportStyles extends WP_UnitTestCas
 	 */
 	private $test_block_name;
 
+	/**
+	 * @var WP_Styles|null
+	 */
+	private $old_wp_styles;
+
 	public function set_up() {
 		parent::set_up();
 		$this->test_block_name = null;
 
-		global $wp_styles;
-		$wp_styles = null;
+		// Use a clean styles queue so tests don't leak registered handles
+		// or inline styles into each other. The default-styles callbacks are
+		// removed because they expect a fully set up instance.
+		$this->old_wp_styles = $GLOBALS['wp_styles'] ?? null;
+		remove_action( 'wp_default_styles', 'wp_default_styles' );
+		remove_action( 'wp_print_styles', 'print_emoji_styles' );
+		$GLOBALS['wp_styles'] = new WP_Styles();
 	}
 
 	public function tear_down() {
@@ -25,8 +35,9 @@ public function tear_down() {
 		}
 		$this->test_block_name = null;
 
-		global $wp_styles;
-		$wp_styles = null;
+		$GLOBALS['wp_styles'] = $this->old_wp_styles;
+		add_action( 'wp_default_styles', 'wp_default_styles' );
+		add_action( 'wp_print_styles', 'print_emoji_styles' );
 
 		parent::tear_down();
 	}
@@ -327,4 +338,107 @@ public function test_css_not_duplicated_on_repeated_renders(): void {
 			'CSS should be enqueued exactly once even when the same block renders multiple times.'
 		);
 	}
+
+	/**
+	 * Tests that custom CSS styles print after block style variation styles,
+	 * regardless of enqueue order, so that custom CSS wins the cascade at
+	 * equal specificity.
+	 *
+	 * @ticket 65641
+	 *
+	 * @covers ::wp_render_custom_css_support_styles
+	 */
+	public function test_custom_css_prints_after_block_style_variation_styles() {
+		wp_register_style( 'wp-block-library', false );
+		wp_register_style( 'global-styles', false );
+
+		$this->test_block_name = 'test/custom-css-print-order';
+		register_block_type(
+			$this->test_block_name,
+			array(
+				'api_version' => 3,
+				'attributes'  => array(
+					'style' => array(
+						'type' => 'object',
+					),
+				),
+				'supports'    => array( 'customCSS' => true ),
+			)
+		);
+
+		$parsed_block = array(
+			'blockName' => 'test/custom-css-print-order',
+			'attrs'     => array(
+				'style' => array(
+					'css' => 'border-style: double;',
+				),
+			),
+		);
+
+		wp_render_custom_css_support_styles( $parsed_block );
+
+		// Mimic the block style variation support registering its per-instance
+		// styles, as done in wp_render_block_style_variation_support_styles().
+		wp_register_style( 'block-style-variation-styles', false, array( 'wp-block-library', 'global-styles' ) );
+		wp_add_inline_style( 'block-style-variation-styles', ':root :where(.is-style-test-variation){border-style: dotted;}' );
+
+		// Enqueue custom CSS first to prove the declared dependency decides
+		// the print order, not the enqueue order.
+		wp_enqueue_style( 'wp-block-custom-css' );
+		wp_enqueue_style( 'block-style-variation-styles' );
+
+		$output = get_echo( 'wp_print_styles' );
+
+		$variation_position  = strpos( $output, 'border-style: dotted' );
+		$custom_css_position = strpos( $output, 'border-style: double' );
+
+		$this->assertNotFalse( $variation_position, 'Block style variation styles should be printed.' );
+		$this->assertNotFalse( $custom_css_position, 'Custom CSS should be printed.' );
+		$this->assertLessThan( $custom_css_position, $variation_position, 'Block style variation styles should print before custom CSS so custom CSS wins ties at equal specificity.' );
+	}
+
+	/**
+	 * Tests that custom CSS still prints when no block style variation styles
+	 * were registered on the page. The `block-style-variation-styles` handle
+	 * is normally registered lazily while rendering a block with a variation,
+	 * and a style with an unregistered dependency is never printed.
+	 *
+	 * @ticket 65641
+	 *
+	 * @covers ::wp_render_custom_css_support_styles
+	 */
+	public function test_custom_css_prints_without_block_style_variation_styles() {
+		wp_register_style( 'wp-block-library', false );
+		wp_register_style( 'global-styles', false );
+
+		$this->test_block_name = 'test/custom-css-no-variations';
+		register_block_type(
+			$this->test_block_name,
+			array(
+				'api_version' => 3,
+				'attributes'  => array(
+					'style' => array(
+						'type' => 'object',
+					),
+				),
+				'supports'    => array( 'customCSS' => true ),
+			)
+		);
+
+		$parsed_block = array(
+			'blockName' => 'test/custom-css-no-variations',
+			'attrs'     => array(
+				'style' => array(
+					'css' => 'color: teal;',
+				),
+			),
+		);
+
+		wp_render_custom_css_support_styles( $parsed_block );
+		wp_enqueue_style( 'wp-block-custom-css' );
+
+		$output = get_echo( 'wp_print_styles' );
+
+		$this->assertStringContainsString( 'color: teal', $output, 'Custom CSS should print even when no block style variation styles exist on the page.' );
+	}
 }