Table thead remains motionless, tbody scrolling (3)

If you need to merge columns in Thead

#tblDataList thead {display:block;}
#tblDataList tbody {display:block;height:600px; overflow-y:scroll; Overflow-x: hidden;}
#tblDataList thead TR {display:table; width:100%; table-layout:fixed;}
#tblDataList tbody TR {display:table; width:100%; table-layout:fixed;}
#tblDataList thead {width:calc (100%-1.17em)}
. ul_inth{padding:0px; margin:0px; border-top:1px solid;}
. Li_inthf{width:33%;list-style:none;float:left;}
. li_inth{Width:33%;list-style:none;float:left; border-left:1px solid;}

<table id= "tbldatalist" cellpadding= "0" cellspacing= "0" >

<thead>

<tr>

<th rowspan= "2" > Time </th>

<th colspan= "3" > Soot <ul class= "ul_inth" ><li class= "LI_INTHF" > Measured (mg/m3) </li><li class= "Li_ Inth "> Conversion (MG/M3) </li><li class=" Li_inth "> Emissions (MG/M3) </li></ul></th>

<th colspan= "3" > Nitrogen oxides <ul class= "Ul_inth" ><li class= "LI_INTHF" > Measured (mg/m3) </li><li class= " Li_inth "> Conversion (MG/M3) </li><li class=" Li_inth "> Emissions (MG/M3) </li></ul></th>

<th colspan= "3" > Sulfur dioxide <ul class= "Ul_inth" ><li class= "LI_INTHF" > Measured (mg/m3) </li><li class= " Li_inth "> Conversion (MG/M3) </li><li class=" Li_inth "> Emissions (MG/M3) </li></ul></th>

<th rowspan= "2" > Barometric <br> (mbar) </th>

<th rowspan= "2" > Smoke temperature <br> (℃) </th>

<th rowspan= "2" > Smoke flow <br> (M/s) </th>

<th rowspan= "2" > Oxygen <br> (%) </th>

<th rowspan= "2" > Standard flow <br> (m3/s) </th></tr></thead>

<tbody>

<tr class= "" ><td>2016-01-01 00:00:00</td><td>12.9900</td><td>16.3800</td ><td>0.0487</td><td>38.8600</td><td>48.9800</td><td>0.1457</td ><td>10.7600</td><td>13.5600</td><td>0.0403</td><td>-0.0700</ td><td>54.4300</td><td>6.3500</td><td>18.6200</td><td>62.4700< /td></tr>

<tr style= "" ><td>2016-01-01 00:05:00</td><td>12.8000</td><td>16.1500</td ><td>0.0480</td><td>38.6700</td><td>48.8000</td><td>0.1450</td ><td>10.4700</td><td>13.2100</td><td>0.0393</td><td>-0.0700</ td><td>54.4000</td><td>6.3500</td><td>18.6200</td><td>62.5100< /td></tr>

</tbody></table>

Table thead remains motionless, tbody scrolling (3)