How To Protect Plugin Display From Being Affected By Theme’s CSS

G.M.’s advice not withstanding, bear in mind that there is no foolproof way of isolating your table from the theme. CSS selectors with more specificity, or with rules that you haven’t accounted for, or with !important rules, will always take precedence. This is actually correct behaviour, as websites should be able to style elements (including your plugin’s output) as they see fit.