public function updateWebBookStyleSheet( $stylesheet = null ) {

		if ( CustomCss::isCustomCss() ) {
			// Compile pressbooks-book web stylesheet when using the *DEPRECATED* Custom CSS theme
			$theme = wp_get_theme( 'pressbooks-book' );
		} else {
			$theme = wp_get_theme( $stylesheet );
		}

		// Populate $url-base variable so that links to images and other assets remain intact
		$overrides = [ '$url-base: "' . $theme->get_stylesheet_directory_uri() . '";' ];
		if ( $this->isCurrentThemeCompatible( 1 ) ) {
			$scss = \Pressbooks\Utility\get_contents( realpath( $this->getDir( $theme ) . '/style.scss' ) );
		} elseif ( $this->isCurrentThemeCompatible( 2 ) || CustomCss::isCustomCss() ) {
			$scss = \Pressbooks\Utility\get_contents( realpath( $this->getDir( $theme ) . '/assets/styles/web/style.scss' ) );
		} else {
			return;
		}

		$custom_styles = $this->getWebPost();
		if ( $custom_styles && ! empty( $custom_styles->post_content ) ) {
			// append the user's custom styles to the theme stylesheet prior to compilation
			$scss .= "\n" . $custom_styles->post_content;
		}

		$css = $this->customize( 'web', $scss, $overrides );

		$css = normalize_css_urls( $css );

		$css_file = $this->sass->pathToUserGeneratedCss() . '/style.css';
		\Pressbooks\Utility\put_contents( $css_file, $css );
	}