diff --git a/src/wp-includes/class-wp-styles.php b/src/wp-includes/class-wp-styles.php
index 9b210b2df9d30..6d47bc15d56fd 100644
--- a/src/wp-includes/class-wp-styles.php
+++ b/src/wp-includes/class-wp-styles.php
@@ -183,12 +183,11 @@ public function do_item( $handle, $group = false ) {
 		$inline_style = $this->print_inline_style( $handle, false );
 
 		if ( $inline_style ) {
-			$inline_style_tag = sprintf(
-				"<style id='%s-inline-css'%s>\n%s\n</style>\n",
-				esc_attr( $handle ),
-				$this->type_attr,
-				$inline_style
-			);
+			$processor = new WP_HTML_Tag_Processor( "<style{$this->type_attr}></style>\n" );
+			$processor->next_tag();
+			$processor->set_attribute( 'id', "{$handle}-inline-css" );
+			$processor->set_modifiable_text( "\n{$inline_style}\n" );
+			$inline_style_tag = $processor->get_updated_html();
 		} else {
 			$inline_style_tag = '';
 		}
@@ -364,12 +363,11 @@ public function print_inline_style( $handle, $display = true ) {
 			return $output;
 		}
 
-		printf(
-			"<style id='%s-inline-css'%s>\n%s\n</style>\n",
-			esc_attr( $handle ),
-			$this->type_attr,
-			$output
-		);
+		$processor = new WP_HTML_Tag_Processor( "<style{$this->type_attr}></style>\n" );
+		$processor->next_tag();
+		$processor->set_attribute( 'id', "{$handle}-inline-css" );
+		$processor->set_modifiable_text( "\n{$output}\n" );
+		echo $processor->get_updated_html();
 
 		return true;
 	}
diff --git a/src/wp-includes/fonts/class-wp-font-face.php b/src/wp-includes/fonts/class-wp-font-face.php
index 07cd3d6de9002..fd66825a0b4e5 100644
--- a/src/wp-includes/fonts/class-wp-font-face.php
+++ b/src/wp-includes/fonts/class-wp-font-face.php
@@ -118,7 +118,13 @@ public function generate_and_print( array $fonts ) {
 			return;
 		}
 
-		printf( $this->get_style_element(), $css );
+		$processor = new WP_HTML_Tag_Processor( "<style class=\"wp-fonts-local\"></style>\n" );
+		$processor->next_tag();
+		foreach ( $this->style_tag_attrs as $name => $value ) {
+			$processor->set_attribute( $name, $value );
+		}
+		$processor->set_modifiable_text( "\n{$css}\n" );
+		echo $processor->get_updated_html();
 	}
 
 	/**
@@ -219,34 +225,6 @@ private function validate_font_face_declarations( array $font_face ) {
 		return $font_face;
 	}
 
-	/**
-	 * Gets the style element for wrapping the `@font-face` CSS.
-	 *
-	 * @since 6.4.0
-	 *
-	 * @return string The style element.
-	 */
-	private function get_style_element() {
-		$attributes = $this->generate_style_element_attributes();
-
-		return "<style class='wp-fonts-local'{$attributes}>\n%s\n</style>\n";
-	}
-
-	/**
-	 * Gets the defined <style> element's attributes.
-	 *
-	 * @since 6.4.0
-	 *
-	 * @return string A string of attribute=value when defined, else, empty string.
-	 */
-	private function generate_style_element_attributes() {
-		$attributes = '';
-		foreach ( $this->style_tag_attrs as $name => $value ) {
-			$attributes .= " {$name}='{$value}'";
-		}
-		return $attributes;
-	}
-
 	/**
 	 * Gets the `@font-face` CSS styles for locally-hosted font files.
 	 *
diff --git a/src/wp-includes/script-loader.php b/src/wp-includes/script-loader.php
index 56986c3d80a79..e968ecb693758 100644
--- a/src/wp-includes/script-loader.php
+++ b/src/wp-includes/script-loader.php
@@ -2417,10 +2417,12 @@ function _print_styles() {
 		echo "<link rel='stylesheet' href='" . esc_attr( $href ) . "'{$type_attr} media='all' />\n";
 
 		if ( ! empty( $wp_styles->print_code ) ) {
-			echo "<style{$type_attr}>\n";
-			echo $wp_styles->print_code;
-			echo sprintf( "\n/*# sourceURL=%s */", rawurlencode( $concat_source_url ) );
-			echo "\n</style>\n";
+			$processor = new WP_HTML_Tag_Processor( "<style{$type_attr}></style>" );
+			$processor->next_tag();
+			$style_tag_contents = "\n{$wp_styles->print_code}\n"
+				. sprintf( "/*# sourceURL=%s */\n", rawurlencode( $concat_source_url ) );
+			$processor->set_modifiable_text( $style_tag_contents );
+			echo $processor->get_updated_html();
 		}
 	}
 
@@ -3217,7 +3219,10 @@ function wp_enqueue_block_support_styles( $style, $priority = 10 ) {
 	add_action(
 		$action_hook_name,
 		static function () use ( $style ) {
-			echo "<style>$style</style>\n";
+			$processor = new WP_HTML_Tag_Processor( "<style></style>\n" );
+			$processor->next_tag();
+			$processor->set_modifiable_text( $style );
+			echo $processor->get_updated_html();
 		},
 		$priority
 	);
diff --git a/src/wp-includes/theme.php b/src/wp-includes/theme.php
index 558bea6ae9e02..b8d35a255d35c 100644
--- a/src/wp-includes/theme.php
+++ b/src/wp-includes/theme.php
@@ -1953,11 +1953,13 @@ function _custom_background_cb() {
 
 		$style .= $image . $position . $size . $repeat . $attachment;
 	}
-	?>
-<style<?php echo $type_attr; ?> id="custom-background-css">
-body.custom-background { <?php echo trim( $style ); ?> }
-</style>
-	<?php
+
+	$processor = new WP_HTML_Tag_Processor( "<style{$type_attr} id=\"custom-background-css\"></style>" );
+	$processor->next_tag();
+
+	$style_tag_content = 'body.custom-background { ' . trim( $style ) . ' }';
+	$processor->set_modifiable_text( "\n{$style_tag_content}\n" );
+	echo $processor->get_updated_html();
 }
 
 /**
@@ -1967,17 +1969,18 @@ function _custom_background_cb() {
  */
 function wp_custom_css_cb() {
 	$styles = wp_get_custom_css();
-	if ( $styles || is_customize_preview() ) :
-		$type_attr = current_theme_supports( 'html5', 'style' ) ? '' : ' type="text/css"';
-		?>
-		<style<?php echo $type_attr; ?> id="wp-custom-css">
-			<?php
-			// Note that esc_html() cannot be used because `div &gt; span` is not interpreted properly.
-			echo strip_tags( $styles );
-			?>
-		</style>
-		<?php
-	endif;
+	if ( ! $styles && ! is_customize_preview() ) {
+		return;
+	}
+
+	$processor = new WP_HTML_Tag_Processor( '<style></style>' );
+	$processor->next_tag();
+	if ( ! current_theme_supports( 'html5', 'style' ) ) {
+		$processor->set_attribute( 'type', 'text/css' );
+	}
+	$processor->set_attribute( 'id', 'wp-custom-css' );
+	$processor->set_modifiable_text( "\n{$styles}\n" );
+	echo $processor->get_updated_html();
 }
 
 /**
diff --git a/tests/phpunit/tests/fonts/font-face/wpFontFace/generateAndPrint.php b/tests/phpunit/tests/fonts/font-face/wpFontFace/generateAndPrint.php
index d10ea500e8707..1f6b07b3cfb0c 100644
--- a/tests/phpunit/tests/fonts/font-face/wpFontFace/generateAndPrint.php
+++ b/tests/phpunit/tests/fonts/font-face/wpFontFace/generateAndPrint.php
@@ -34,7 +34,11 @@ public function test_should_generate_and_print_given_fonts( array $fonts, $expec
 		$style_element   = "<style class='wp-fonts-local' type='text/css'>\n%s\n</style>\n";
 		$expected_output = sprintf( $style_element, $expected );
 
-		$this->expectOutputString( $expected_output );
-		$font_face->generate_and_print( $fonts );
+		$output = get_echo(
+			function () use ( $font_face, $fonts ) {
+				$font_face->generate_and_print( $fonts );
+			}
+		);
+		$this->assertEqualHTML( $expected_output, $output );
 	}
 }
diff --git a/tests/phpunit/tests/fonts/font-face/wpPrintFontFaces.php b/tests/phpunit/tests/fonts/font-face/wpPrintFontFaces.php
index 2fa64559c2049..1d6ef663c5f22 100644
--- a/tests/phpunit/tests/fonts/font-face/wpPrintFontFaces.php
+++ b/tests/phpunit/tests/fonts/font-face/wpPrintFontFaces.php
@@ -37,8 +37,12 @@ public function test_should_not_print_when_no_fonts() {
 	public function test_should_print_given_fonts( array $fonts, $expected ) {
 		$expected_output = $this->get_expected_styles_output( $expected );
 
-		$this->expectOutputString( $expected_output );
-		wp_print_font_faces( $fonts );
+		$output = get_echo(
+			function () use ( $fonts ) {
+				wp_print_font_faces( $fonts );
+			}
+		);
+		$this->assertEqualHTML( $expected_output, $output );
 	}
 
 	public function test_should_escape_tags() {
@@ -60,9 +64,13 @@ public function test_should_escape_tags() {
 </style>
 
 CSS;
-		$this->expectOutputString( $expected_output );
 
-		wp_print_font_faces( $fonts );
+		$output = get_echo(
+			function () use ( $fonts ) {
+				wp_print_font_faces( $fonts );
+			}
+		);
+		$this->assertEqualHTML( $expected_output, $output );
 	}
 
 	public function test_should_print_fonts_in_merged_data() {
@@ -71,8 +79,8 @@ public function test_should_print_fonts_in_merged_data() {
 		$expected        = $this->get_expected_fonts_for_fonts_block_theme( 'font_face_styles' );
 		$expected_output = $this->get_expected_styles_output( $expected );
 
-		$this->expectOutputString( $expected_output );
-		wp_print_font_faces();
+		$output = get_echo( 'wp_print_font_faces' );
+		$this->assertEqualHTML( $expected_output, $output );
 	}
 
 	private function get_expected_styles_output( $styles ) {
diff --git a/tests/phpunit/tests/fonts/font-face/wpPrintFontFacesFromStyleVariations.php b/tests/phpunit/tests/fonts/font-face/wpPrintFontFacesFromStyleVariations.php
index a59ba882a4e86..5dd6304fd2f7b 100644
--- a/tests/phpunit/tests/fonts/font-face/wpPrintFontFacesFromStyleVariations.php
+++ b/tests/phpunit/tests/fonts/font-face/wpPrintFontFacesFromStyleVariations.php
@@ -43,8 +43,8 @@ public function test_should_print_fonts_in_style_variations() {
 		$expected        = $this->get_custom_style_variations( 'expected_styles' );
 		$expected_output = $this->get_expected_styles_output( $expected );
 
-		$this->expectOutputString( $expected_output );
-		wp_print_font_faces_from_style_variations();
+		$output = get_echo( 'wp_print_font_faces_from_style_variations' );
+		$this->assertEqualHTML( $expected_output, $output );
 	}
 
 	private function get_expected_styles_output( $styles ) {