If the object has an ID, lets say mainTable, you can edit that table only by using
<style>
#mainTable {
border: 1px solid;
}
</style>
Or if you want the same style for more than one table you can create a class, and call for that class in each element you want to inherit the style
<style>
.tabless{
border: 5px solid;
}
</style>
<table id="table1" class="tabless"></table>
<table id="mainTable"></table>
<table id="table2" class="tabless"></table>
Thus table1 and table2 have a different border than mainTable.