title: Adding a style element within another element and having the styles only apply to the parent?
body: <p>Suppose a generated fragment of HTML and CSS where the CSS should not apply outside of the fragment.</p>
  <pre><code>&lt;div class=&quot;text&quot;&gt;I am outside and should not be red.&lt;/div&gt;
  &lt;div&gt;
    &lt;div class=&quot;text&quot;&gt;I am inside and should be red.&lt;/div&gt;
  
    &lt;style type=&quot;text/css&quot;&gt;
      .text {
        color: red;
      }
    &lt;/style&gt;
  &lt;/div&gt;
  </code></pre>
  <p>Which produces:</p>
  <p><a href="https://i.stack.imgur.com/BOmLG.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/BOmLG.png" alt="example" /></a></p>
  <p>How can the <code>&lt;style&gt;</code> tag be altered to only apply to its containing element (<code>&lt;div&gt;</code>) and its children? Consider that a unique id/class cannot be used, so this solution is not valid in this case, although it would naturally produce the desired result:</p>
  <pre><code>&lt;div class=&quot;text&quot;&gt;I am outside and should not be red.&lt;/div&gt;
  &lt;div class=&quot;sandbox&quot;&gt;
    &lt;div class=&quot;text&quot;&gt;I am inside and should be red.&lt;/div&gt;
  
    &lt;style type=&quot;text/css&quot;&gt;
      .sandbox .text {
        color: red;
      }
    &lt;/style&gt;
  &lt;/div&gt;
  </code></pre>
  <p>The HTML and Style (and JS) will be entered standalone and will be wrapped and injected into the DOM at-will. So the goal is that this injected chunk is &quot;sandboxed&quot; to the outermost element of the chunk. And I don't want to depend on the author to correctly apply unique selectors to all of their CSS classes -- you know, because people make mistakes. Instead, I want to automatically scope the  within the chunk to the generated parent element which contains it.</p>
  <p>Suppose the &quot;chunk&quot; is as below:</p>
  <pre><code>&lt;div class=&quot;text&quot;&gt;I am inside and should be red.&lt;/div&gt;
  
  &lt;style type=&quot;text/css&quot;&gt;
    .text {
      color: red;
    }
  &lt;/style&gt;
  </code></pre>
  <p>The &quot;server&quot; would return a wrapped chunk like this (note the wrapper <code>&lt;div&gt;</code>):</p>
  <pre><code>&lt;div&gt;
    &lt;div class=&quot;text&quot;&gt;I am inside and should be red.&lt;/div&gt;
  
    &lt;style type=&quot;text/css&quot;&gt;
      .text {
        color: red;
      }
    &lt;/style&gt;
  &lt;/div&gt;
  </code></pre>
  <p>The part that is missing is how to &quot;scope&quot; any <code>&lt;style&gt;</code> elements within the chunk so they only apply to the wrapper.</p>
  <p>It appears that this used to be possible via the <code>scoped</code> <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/style#attr-scoped" rel="nofollow noreferrer">attribute</a>, but it is deprecated. It appears that I can polyfill this feature, which is what I will do for now, but I am curious if there is another solution.</p>