[css-color-3] Replace <td><em> with <th> since styling for former is no longer supported.

https://lists.w3.org/Archives/Member/w3c-css-wg/2014JulSep/0018.html
explains that the styles have been removed for default.css

Author: dbaron

css-color-3/Overview.html

@@ -374,42 +374,42 @@ <h3 id=foreground><span class=secno>3.1. </span>Foreground color: the ‘<a
   <table class=propdef>
    <tbody>
     <tr>
-     <td><em>Name:</em>
+     <th>Name:
 
      <td><dfn id=color0>color</dfn>
 
     <tr>
-     <td><em>Value:</em>
+     <th>Value:
 
      <td>&lt;color&gt; | inherit
 
     <tr>
-     <td><em>Initial:</em>
+     <th>Initial:
 
      <td>depends on user agent
 
     <tr>
-     <td><em>Applies to:</em>
+     <th>Applies to:
 
      <td>all elements
 
     <tr>
-     <td><em>Inherited:</em>
+     <th>Inherited:
 
      <td>yes
 
     <tr>
-     <td><em>Percentages:</em>
+     <th>Percentages:
 
      <td>N/A
 
     <tr>
-     <td><em>Media:</em>
+     <th>Media:
 
      <td>visual
 
     <tr>
-     <td><em>Computed value:</em>
+     <th>Computed value:
 
      <td>
       <ul>
@@ -467,42 +467,42 @@ <h3 id=transparency><span class=secno>3.2. </span>Transparency: the ‘<a
   <table class=propdef>
    <tbody>
     <tr>
-     <td><em>Name:</em>
+     <th>Name:
 
      <td><dfn id=opacity>opacity</dfn>
 
     <tr>
-     <td><em>Value:</em>
+     <th>Value:
 
      <td>&lt;alphavalue&gt; | inherit
 
     <tr>
-     <td><em>Initial:</em>
+     <th>Initial:
 
      <td>1
 
     <tr>
-     <td><em>Applies to:</em>
+     <th>Applies to:
 
      <td>all elements
 
     <tr>
-     <td><em>Inherited:</em>
+     <th>Inherited:
 
      <td>no
 
     <tr>
-     <td><em>Percentages:</em>
+     <th>Percentages:
 
      <td>N/A
 
     <tr>
-     <td><em>Media:</em>
+     <th>Media:
 
      <td>visual
 
     <tr>
-     <td><em>Computed value:</em>
+     <th>Computed value:
 
      <td>The same as the specified value after clipping the
       &lt;alphavalue&gt; to the range [0.0,1.0].

css-color-3/Overview.src.html

@@ -203,35 +203,35 @@ <h3 id="foreground">Foreground color: the 'color' property</h3>
 <table class="propdef">
   <tbody>
     <tr>
-      <td><em>Name:</em></td>
+      <th>Name:</th>
       <td><dfn id="color0">color</dfn></td>
     </tr>
     <tr>
-      <td><em>Value:</em></td>
+      <th>Value:</th>
       <td>&lt;color&gt; | inherit</td>
     </tr>
     <tr>
-      <td><em>Initial:</em></td>
+      <th>Initial:</th>
       <td>depends on user agent</td>
     </tr>
     <tr>
-      <td><em>Applies&nbsp;to:</em></td>
+      <th>Applies&nbsp;to:</th>
       <td>all elements</td>
     </tr>
     <tr>
-      <td><em>Inherited:</em></td>
+      <th>Inherited:</th>
       <td>yes</td>
     </tr>
     <tr>
-      <td><em>Percentages:</em></td>
+      <th>Percentages:</th>
       <td>N/A</td>
     </tr>
     <tr>
-      <td><em>Media:</em></td>
+      <th>Media:</th>
       <td>visual</td>
     </tr>
     <tr>
-      <td><em>Computed value:</em></td>
+      <th>Computed value:</th>
       <td>
       <ul>
       <li>The computed value for basic color keywords, RGB hex values and extended color keywords
@@ -278,35 +278,35 @@ <h3 id="transparency">Transparency: the 'opacity' property</h3>
 <table class="propdef">
   <tbody>
     <tr>
-      <td><em>Name:</em></td>
+      <th>Name:</th>
       <td><dfn id="opacity">opacity</dfn></td>
     </tr>
     <tr>
-      <td><em>Value:</em></td>
+      <th>Value:</th>
       <td>&lt;alphavalue&gt; | inherit</td>
     </tr>
     <tr>
-      <td><em>Initial:</em></td>
+      <th>Initial:</th>
       <td>1</td>
     </tr>
     <tr>
-      <td><em>Applies&nbsp;to:</em></td>
+      <th>Applies&nbsp;to:</th>
       <td>all elements</td>
     </tr>
     <tr>
-      <td><em>Inherited:</em></td>
+      <th>Inherited:</th>
       <td>no</td>
     </tr>
     <tr>
-      <td><em>Percentages:</em></td>
+      <th>Percentages:</th>
       <td>N/A</td>
     </tr>
     <tr>
-      <td><em>Media:</em></td>
+      <th>Media:</th>
       <td>visual</td>
     </tr>
     <tr>
-      <td><em>Computed value:</em></td>
+      <th>Computed value:</th>
       <td>The same as the specified value after clipping the &lt;alphavalue&gt; to the range [0.0,1.0]. </td>
     </tr>
   </tbody>