E).keys()]
          .map(x => `--x${x}:a b c d e f g;`).join('\n')}
      }
    `);
  }

  return `
    div {
      ${rules.join('\n')}
    }
  `
}

let globalCounter = 0;
const stylesheetText = makeStyle();
let stylesheet = new CSSStyleSheet();

PerfTestRunner.measureTime({
    description: 'Many nested rules that look like declarations',
    run: () => {
      // This is a parsing test: we don't care about style recalc.
      // We append a rule based on globalCounter to prevent caching
      // on the s