added html solution for testing - responsive-web-design/applied-visual-design/decrease-the-opacity-of-an-element (#35516)

* added html solution for testing

* fix: corrected invalid solution

curriculum/challenges/english/01-responsive-web-design/applied-visual-design/decrease-the-opacity-of-an-element.english.md

@@ -91,7 +91,52 @@ tests:
 ## Solution
 <section id='solution'>
 
-```js
-// solution required
+```html
+<style>
+  h4 {
+    text-align: center;
+    background-color: rgba(45, 45, 45, 0.1);
+    padding: 10px;
+    font-size: 27px;
+  }
+  p {
+    text-align: justify;
+  }
+  .links {
+    text-align: left;
+    color: black;
+    opacity: 0.7;
+  }
+  #thumbnail {
+    box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);
+  }
+  .fullCard {
+    width: 245px;
+    border: 1px solid #ccc;
+    border-radius: 5px;
+    margin: 10px 5px;
+    padding: 4px;
+  }
+  .cardContent {
+    padding: 10px;
+  }
+  .cardText {
+    margin-bottom: 30px;
+  }
+
+</style>
+<div class="fullCard" id="thumbnail">
+  <div class="cardContent">
+    <div class="cardText">
+      <h4>Alphabet</h4>
+      <hr>
+      <p><em>Google was founded by Larry Page and Sergey Brin while they were <u>Ph.D. students</u> at <strong>Stanford University</strong>.</em></p>
+    </div>
+    <div class="cardLinks">
+      <a href="https://en.wikipedia.org/wiki/Larry_Page" target="_blank" class="links">Larry Page</a><br><br>
+      <a href="https://en.wikipedia.org/wiki/Sergey_Brin" target="_blank" class="links">Sergey Brin</a>
+    </div>
+  </div>
+</div>
 ```
 </section>