regenerate html doc
diff --git a/docs/awesome_table_in_html.html b/docs/awesome_table_in_html.html
index c0c276f..6d12800 100644
--- a/docs/awesome_table_in_html.html
+++ b/docs/awesome_table_in_html.html
@@ -11,7 +11,7 @@
<meta name="author" content="Hao Zhu" />
-<meta name="date" content="2017-05-24" />
+<meta name="date" content="2017-05-26" />
<title>Create Awesome HTML Table with knitr::kable and kableExtra</title>
@@ -217,7 +217,7 @@
<h1 class="title toc-ignore">Create Awesome HTML Table with knitr::kable and kableExtra</h1>
<h4 class="author"><em>Hao Zhu</em></h4>
-<h4 class="date"><em>2017-05-24</em></h4>
+<h4 class="date"><em>2017-05-26</em></h4>
</div>
@@ -1603,14 +1603,20 @@
<thead>
<tr>
<th style="border-bottom:hidden"></th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 1
+</div>
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 2
+</div>
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 3
+</div>
</th>
</tr>
<tr>
@@ -1765,29 +1771,41 @@
<thead>
<tr>
<th style="border-bottom:hidden"></th>
-<th style="text-align:center;" colspan="6">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="6">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 6
+</div>
</th>
</tr>
<tr>
<th style="border-bottom:hidden"></th>
-<th style="text-align:center;" colspan="4">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="4">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 4
+</div>
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 5
+</div>
</th>
</tr>
<tr>
<th style="border-bottom:hidden"></th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 1
+</div>
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 2
+</div>
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="2">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 3
+</div>
</th>
</tr>
<tr>
@@ -2447,11 +2465,15 @@
<thead>
<tr>
<th style="border-bottom:hidden"></th>
-<th style="text-align:center;" colspan="3">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="3">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 1<sup>†</sup>
+</div>
</th>
-<th style="text-align:center;" colspan="3">
+<th style="text-align:center; border-bottom:hidden; padding-bottom:0; padding-left:3px;padding-right:3px;" colspan="3">
+<div style="border-bottom: 1px solid #ddd;padding-bottom: 5px;">
Group 2<sup>‡</sup>
+</div>
</th>
</tr>
<tr>