improve html grouped header row
diff --git a/docs/awesome_table_in_html.html b/docs/awesome_table_in_html.html
index 949666c..d88d6fc 100644
--- a/docs/awesome_table_in_html.html
+++ b/docs/awesome_table_in_html.html
@@ -1602,15 +1602,14 @@
<table class="table table-striped" style="margin-left: auto; margin-right: auto;">
<thead>
<tr>
-<th style="text-align:center;" colspan="1">
-</th>
-<th style="text-align:center;" colspan="2">
+<th style="border-bottom:hidden"></th>
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 1
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 2
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 3
</th>
</tr>
@@ -1765,32 +1764,29 @@
<table class="table table-striped table-bordered" style="margin-left: auto; margin-right: auto;">
<thead>
<tr>
-<th style="text-align:center;" colspan="1">
-</th>
-<th style="text-align:center;" colspan="6">
+<th style="border-bottom:hidden"></th>
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="6">
Group 6
</th>
</tr>
<tr>
-<th style="text-align:center;" colspan="1">
-</th>
-<th style="text-align:center;" colspan="4">
+<th style="border-bottom:hidden"></th>
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="4">
Group 4
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 5
</th>
</tr>
<tr>
-<th style="text-align:center;" colspan="1">
-</th>
-<th style="text-align:center;" colspan="2">
+<th style="border-bottom:hidden"></th>
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 1
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 2
</th>
-<th style="text-align:center;" colspan="2">
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="2">
Group 3
</th>
</tr>
@@ -2450,12 +2446,11 @@
</caption>
<thead>
<tr>
-<th style="text-align:center;" colspan="1">
-</th>
-<th style="text-align:center;" colspan="3">
+<th style="border-bottom:hidden"></th>
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="3">
Group 1<sup>†</sup>
</th>
-<th style="text-align:center;" colspan="3">
+<th style="text-align:center;border-collapse: separate !important; margin-right: 10px !important;" colspan="3">
Group 2<sup>‡</sup>
</th>
</tr>