title: How to customise the textMateRules for multiple themes in VS Code?
body: <p>In <strong>VS Code</strong>, I'd like to customise some <code>textMateRules</code> the same for multiple themes. For example, both for <code>Atom One Dark</code> and <code>Default Dark+</code> but without affecting any of the other themes, I'd like to make the <code>keyword</code>s <em>italic</em>. I can achieve this by duplicating the same settings twice separately for each theme as below</p>
  
  <pre class="lang-json prettyprint-override"><code>  "editor.tokenColorCustomizations": {
      "[Atom One Dark]": {
        "textMateRules": [
          {
            "scope": [ "keyword" ],
            "settings": { "fontStyle": "italic" }
          }
        ]
      },
      "[Default Dark+]": {
        "textMateRules": [
          {
            "scope": [ "keyword" ],
            "settings": { "fontStyle": "italic" }
          }
        ]
      }
    }
  </code></pre>
  
  <p>How can I only need to set up once for both, without duplicating the rules, especially if there are a lot same rules for the multiple themes? Something like the below (<strong><em>but which doesn't work though</em></strong>)</p>
  
  <pre class="lang-json prettyprint-override"><code>  "editor.tokenColorCustomizations": {
      "[Atom One Dark] [Default Dark+]": {
        "textMateRules": [
          {
            "scope": [ "keyword" ],
            "settings": { "fontStyle": "italic" }
          }
        ]
      }
    }
  </code></pre>