Source

File: wp-includes/sitemaps/class-wp-sitemaps-stylesheet.php

public function get_stylesheet_css() {
		$text_align = is_rtl() ? 'right' : 'left';

		$css = <<<EOF

					body {
						font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Oxygen-Sans, Ubuntu, Cantarell, "Helvetica Neue", sans-serif;
						color: #444;
					}

					#sitemap__table {
						border: solid 1px #ccc;
						border-collapse: collapse;
					}

			 		#sitemap__table tr td.loc {
						/*
						 * URLs should always be LTR.
						 * See https://core.trac.wordpress.org/ticket/16834
						 * and https://core.trac.wordpress.org/ticket/49949
						 */
						direction: ltr;
					}

					#sitemap__table tr th {
						text-align: {$text_align};
					}

					#sitemap__table tr td,
					#sitemap__table tr th {
						padding: 10px;
					}

					#sitemap__table tr:nth-child(odd) td {
						background-color: #eee;
					}

					a:hover {
						text-decoration: none;
					}

EOF;

		/**
		 * Filters the CSS only for the sitemap stylesheet.
		 *
		 * @since 5.5.0
		 *
		 * @param string $css CSS to be applied to default XSL file.
		 */
		return apply_filters( 'wp_sitemaps_stylesheet_css', $css );
	}