Override CSS Style in PHP Page

I am currently writing an addon module for our Billing Software, and the modules automatically inherit the template's CSS when you use any of the elements. For example, I use the "datatable" element for my tables, and it inherits the CSS style depending upon what template the user is currently using.

I want to hide the inner border that the "datatable" element has, and I am using <style> tags to put all of my CSS in the module code. I am not quite sure how I can do this, but here is what the CSS looks like from the billing software's template style.css file.

table.form {
border: 1px solid #B8CBE7;
background-color: #fff;
padding: 0px;
}
table.form td.fieldlabel {
text-align: right;
font-weight: bold;
padding: 5px;
background-color: #E4ECF8;
}
table.form td.fieldarea {
text-align: left;
padding: 5px;
border-bottom: 1px dashed #ccc;
}
.tablebg {
background-color: #e9e9e9;
}
table.datatable {
padding: 0;
margin: 0;
}
table.datatable th {
background-color: #f3f3f3;
font-weight: bold;
text-align: center;
}
table.datatable td {
background-color: #fff;
text-align: center;
}
table.datatable tr.rowhighlight td {
background-color: #EFF2F9;
}
table.datatable tr:hover td {
background-color: #EFF2F9;
}

You can define the same **datatable** class again and set it's border as 0. You will just need to ensure this new css definition comes after the actual one

table.datatable {
border: 0px;
}

try append this line in CSS stylesheet:

`.datatable{
border: 0 !important;
}`