html - Border style do not work with sticky position element

Question

I don't know why my border style do not work with position: sticky; attribute. I would like to set border styles on my sticky table header. But I don't want to use the transparent background colour. How can I achieve it? Here are sample codes for my problem and JSFiddle Link

#wrapper {
  width: 400px;
  height: 200px;
  overflow: auto;
}

table {
  width: 100%;
  text-align: center;
  border-collapse: collapse;
}

table tr th,
table tr td {
  border: 2px solid;
}

table thead th {
  position: -webkit-sticky;
  position: sticky;
  top: 0;
  background-color: #edecec;
}

<div id="wrapper">
  <table>
    <thead>
      <tr>
        <th>A</th>
        <th>B</th>
        <th>C</th>
        <th>D</th>
        <th>E</th>
      </tr>
    </thead>
    <tr>
      <td>1</td>
      <td>1</td>
      <td>1</td>
      <td>1</td>
      <td>1</td>
    </tr>
    <tr>
      <td>2</td>
      <td>2</td>
      <td>2</td>
      <td>2</td>
      <td>2</td>
    </tr>
    <tr>
      <td>3</td>
      <td>3</td>
      <td>3</td>
      <td>3</td>
      <td>3</td>
    </tr>
    <tr>
      <td>4</td>
      <td>4</td>
      <td>4</td>
      <td>4</td>
      <td>4</td>
    </tr>
    <tr>
      <td>5</td>
      <td>5</td>
      <td>5</td>
      <td>5</td>
      <td>5</td>
    </tr>
    <tr>
      <td>6</td>
      <td>6</td>
      <td>6</td>
      <td>6</td>
      <td>6</td>
    </tr>
    <tr>
      <td>7</td>
      <td>7</td>
      <td>7</td>
      <td>7</td>
      <td>7</td>
    </tr>
    <tr>

      <td>8</td>
      <td>8</td>
      <td>8</td>
      <td>8</td>
      <td>8</td>
    </tr>
    <tr>
      <td>9</td>
      <td>9</td>
      <td>9</td>
      <td>9</td>
      <td>9</td>
    </tr>
    <tbody>
    </tbody>
  </table>
</div>

Answer 1

The problem occurs because of the use of border-collapse: collapse. When browsers collapse the borders, the top and bottom border on the <th> must be getting applied to surrounding elements—the top border to the <table> and the bottom border to the following <tr>.

If you use border-collapse: separate and fashion your borders to sit on one side, the borders will truly attach to the <th>, stay fixed as expected, and appear collapsed.

Here are example styles that can be applied to your HTML snippet.

#wrapper {
  width: 400px;
  height: 200px;
  overflow: auto;
}

table {
  width: 100%;
  text-align: center;
  border-collapse: separate; /* Don't collapse */
  border-spacing: 0;
}

table th {
  /* Apply both top and bottom borders to the <th> */
  border-top: 2px solid;
  border-bottom: 2px solid;
  border-right: 2px solid;
}

table td {
  /* For cells, apply the border to one of each side only (right but not left, bottom but not top) */
  border-bottom: 2px solid;
  border-right: 2px solid;
}

table th:first-child,
table td:first-child {
  /* Apply a left border on the first <td> or <th> in a row */
  border-left: 2px solid;
}

table thead th {
  position: sticky;
  top: 0;
  background-color: #edecec;
}