tableに謎のpadding

tableのコーディングをしていたところ、よくわからないpaddingが入ります。なぜでしょうか？

HTML
1
2
3<table>
4            <tbody>
5                <tr>
6                    <td colspan="3" class="table-tit">
7                        <p>受講期間<span class="till-number">1</span>ヶ月</p>
8                    </td>
9                </tr>
10                <tr>
11                    <th class="table-h">
12                        <p class="table-category">社会人</p>
13                    </th>
14                    <td colspan="2" class="table-b">
15                        <p>¥128,000<span class="tax">(税別)</span></p>
16                    </td>
17                </tr>
18                <tr>
19                    <th class="table-h">
20                        <p class="table-category">学生</p>
21                    </th>
22                    <td colspan="2" class="table-b">
23                        <p>¥99,800<span class="tax">(税別)</span></p>
24                    </td>
25                </tr>
26            </tbody>
27        </table>

CSS
1
2
3table {
4    width: 320px;
5    height: 146px;
6    margin: 39px auto 0;
7    text-align: center;
8}
9
10.table-tit {
11    width: 320px;
12    height: 50px;
13    background-color: #f2f2f2;
14    border: 1px solid #ddd;
15}
16
17.table-tit p {
18    font-size: 20px;
19    line-height: 48px;
20    font-weight: 500;
21}
22
23.till-number {
24    font-size: 24px;
25    font-weight: 600;
26    display: inline-block;
27    margin-left: 5px;
28}
29
30.table-h {
31    width: 117px;
32    height: 48px;
33    border-left: 1px solid #ddd;
34    border-right: 1px solid #ddd; 
35    border-bottom: 1px solid #ddd;
36    padding: 0;
37
38}
39
40.table-category {
41    font-size: 20px;
42    line-height: 47px;
43    font-weight: 700;
44    color: #64678c;
45}
46
47.table-b {
48    width: 203px;
49    height: 48px;
50    border-right: 1px solid #ddd; 
51    border-bottom: 1px solid #ddd;
52    padding: 0;
53}