Octal literals are not allowed in strict mode

You need to escape it

.text::after {
  content: "\\00a0\\00a0";  // now it's just a simple plain string
}

---

"use strict" is a new feature introduced in JavaScript 1.8.5 (ECMAScript version 5).

In which,

• Octal numeric literals are not allowed
• Escape characters are not allowed
• see more...

Or you can add u (unicode) before the \.

  .text::after {
    content: "\u00a0\u00a0"
  }