Make the tables prettier by using the default style. (#163)

"simple" css class was defined nowhere anyway.

index.html

@@ -161,7 +161,7 @@ <h3>
       <p>
         The following internal slots are added to the {{Document}} interface.
       </p>
-      <table class="simple">
+      <table class="def">
         <thead>
           <tr>
             <th>
@@ -413,7 +413,7 @@ <h3>
       <h4>
         Foldables
       </h4>
-      <table class="simple">
+      <table class="def">
         <caption>
           Posture values for foldable devices
         </caption>
@@ -759,7 +759,7 @@ <h2>
         [[[#algorithms]]], [=top-level traversables=] must have the following
         internal slots:
       </p>
-      <table class="simple">
+      <table class="def">
         <thead>
           <tr>
             <th>
@@ -799,7 +799,7 @@ <h3>
       <h4>
         Set device posture
       </h4>
-      <table class="simple">
+      <table class="def">
         <tr>
           <th>
             HTTP Method
@@ -821,7 +821,7 @@ <h4>
         This [=extension command=] changes device posture to a specific
         {{DevicePostureType}}.
       </p>
-      <table class="simple">
+      <table class="def">
         <caption>
           Properties of the parameters argument used by this algorithm
         </caption>
@@ -881,7 +881,7 @@ <h4>
       <h4>
         Clear device posture
       </h4>
-      <table class="simple">
+      <table class="def">
         <tr>
           <th>
             HTTP Method