This can be achieved by merging you checkbox code with the table. Here, I have updated the code.
tbody>tr>td:not(:first-child) {
background-color: teal;
padding:20px;
}
tbody>tr>td{
padding-right:5px;
}
thead>tr>td{
text-align: center;
}
table{border-collapse: collapse;}
<div class="table-container">
<table class="table">
<thead>
<tr>
<td></td>
<td>1</td>
<td>2</td>
<td>3</td>
<td>4</td>
</tr>
</thead>
<tbody>
<tr class="letter">
<td>A</td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
</tr>
<tr class="letter">
<td>B</td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
</tr>
<tr class="letter">
<td>C</td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
</tr>
<tr class="letter">
<td>D</td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
<td><input type="checkbox" class="business-bx"></td>
</tr>
</tbody>
</table>
</div>