added reference on transition 3D

Author: khan4019

css.html

@@ -292,17 +292,18 @@ <h2>14. shadow DOM</h2>
   <p><strong>Answer:</strong> encapsulate part of a DOM. hide subtree. you can have same ID in different shadow DOM. Polymers uses it. This way your DOM becomes reusable and u dont have to do iframe. if interviewer is not happy with your answer give him the links and tell him to spend a weekend on reading.</p>
   <p>ref: <a href="http://www.w3.org/TR/shadow-dom/#introduction">W3: shadow-DOM</a>, <a href="http://www.html5rocks.com/en/tutorials/webcomponents/shadowdom/">html5rock: shadow DOM</a></p> 
 </div>
-<!-- <div id="semantic_html">
-  <h2>15. semantic</h2>
-  <p><strong>Question:</strong> What is semantic HTML?</p>
-  <p><strong>Answer:</strong> Semantic HTML, or "semantically-correct HTML", is HTML where the tags used to structure content are selected and applied appropriately to the meaning of the content.</p>
-  <p>for example, &lt;b&gt;&lt;/b&gt; (for bold), and &lt;i&gt;&lt;/i&gt; (for italic) should never be used, because they&#x2019;re to do with formatting, not with the meaning or structure of the content. Instead, use the replacements &lt;strong&gt;&lt;/strong&gt; and &lt;em&gt;&lt;/em&gt; (meaning emphasis), which by default will turn text bold and italic (but don&#x2019;t have to do so in all browsers), while adding meaning to the structure of the content.</p>
-  <p>ref: <a href="http://en.wikipedia.org/wiki/Semantic_HTML">Wiki: semantic HTML</a> </p>
-</div> -->
+<div id="semantic_html">
+  <h2>15. transition</h2>
+  <p><strong>Question:</strong> What do u know about tranisition 3D?</p>
+  <p><strong>Answer:</strong> .</p>
+  
+  <p>ref: <a href="https://developer.mozilla.org/en-US/docs/Web/Guide/CSS/Using_CSS_transitions">css transition</a> <a href="http://www.html5rocks.com/en/tutorials/3d/css/">transition and 3D</a></p>
+</div>
 <div>
 
 <h2>temporary list of questions</h2>
 <ul>  
+  <li>opacity <a href="http://www.youtube.com/watch?v=iYdfj0XxoMY">paul irish</a></li>
   <li>transition 3D</li>
   <li>text effect in css3</li>  
   <li>reset css</li>