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…