如何使 Bootstrap 下拉菜单显示在粘性表格标题的前面？

Question

I followed a CSS Tricks tutorial to get a table with a sticky header and first column, and tried adding a Bootstrap dropdown inside of the first column.

Problem is, the dropdown shows up in front of the parent cell but behind all of the others of the first column:

I've tried changing the position of the cell to relative, switching the z-index of the dropdown menu to a higher value but the dropdown is still behind the first column.

Here's a JSFiddle with a minimum, reproducible example: https://jsfiddle.net/maxencelav/hwsrcmL6/14/

 @import url("https://fonts.googleapis.com/css2?family=Fraunces:ital,wght@0,700;1,200&display=swap"); table { font-family: "Fraunces", serif; font-size: 125%; white-space: nowrap; margin: 3px; border: none; border-collapse: separate; border-spacing: 0; table-layout: fixed; border: 1px solid black; } table td, table th { border: 1px solid black; padding: 0.5rem 1rem; } table thead th { padding: 3px; position: sticky; top: 0; z-index: 1; width: 25vw; background: white; } table td { background: #fff; padding: 4px 5px; text-align: center; } table tbody th { font-weight: 100; font-style: italic; text-align: left; position: relative; } table thead th:first-child { position: sticky; left: 0; z-index: 2; } table tbody th { position: sticky; left: 0; background: white; z-index: 1; } caption { text-align: left; padding: 0.25rem; position: sticky; left: 0; } [role="region"][aria-labelledby][tabindex] { width: 100%; max-height: 98vh; overflow: auto; } #team-cell-container { display: grid; grid-template-columns: 1fr auto; align-items: center; margin: 0; gap: 5px; }

 <script src="https://code.jquery.com/jquery-3.4.1.slim.js"></script> <link href="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/css/bootstrap.css" rel="stylesheet" /> <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.16.0/umd/popper.js"></script> <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.4.1/js/bootstrap.js"></script> <link href="https://stackpath.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.css" rel="stylesheet" /> <:-- Based off https.//css-tricks.com/a-table-with-both-a-sticky-header-and-a-sticky-first-column/ --> <table> <thead> <tr> <th>Teams</th> <th>1</th> <th>2</th> <th>3</th> <th>4</th> <th>5</th> <th>6</th> <th>7</th> <th>8</th> <th>9</th> <th>Runs</th> </tr> </thead> <tbody> <tr> <th> <div id="team-cell-container"> Milwaukee Brewers <div class="dropdown"> <i class="fa fa-cog" type="button" id="dropdown-item" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"></i> <div class="dropdown-menu" aria-labelledby="dropdown-item"> <a class="dropdown-item" href="#">Action</a> <a class="dropdown-item" href="#">Another action</a> <a class="dropdown-item" href="#">Something else here</a> </div> </div> </div> </th> <td>2</td> <td>1</td> <td>4</td> <td>0</td> <td>3</td> <td>1</td> <td>1</td> <td>0</td> <td>1</td> <td>13</td> </tr> <tr> <th>Los Angles Dodgers</th> <td>4</td> <td>2</td> <td>0</td> <td>0</td> <td>3</td> <td>2</td> <td>4</td> <td>2</td> <td>3</td> <td>20</td> </tr> <tr> <th>New York Mets</th> <td>0</td> <td>1</td> <td>2</td> <td>0</td> <td>0</td> <td>2</td> <td>4</td> <td>0</td> <td>3</td> <td>12</td> </tr> <tr> <th>St. Louis Cardinals</th> <td>3</td> <td>4</td> <td>1</td> <td>3</td> <td>2</td> <td>4</td> <td>3</td> <td>2</td> <td>3</td> <td>25</td> </tr> </tbody> </table>

Answer 1

This is problem with CSS position and z-index . It was explained by this question . (Or see my testing ).

To make position: absolute with high z-index appears on top of other relative, you have to set z-index of the others to be lower than z-index of the parent dropdown. This confirmed work by this answer .

First, add some identity to your table.

<!-- Based off https://css-tricks.com/a-table-with-both-a-sticky-header-and-a-sticky-first-column/ -->

<table id="my-table">
  <thead>
    <tr>
      <th>Teams</th>
      <th>1</th>
      <th>2</th>
      <th>3</th>
      <th>4</th>
      <th>5</th>
      <th>6</th>
      <th>7</th>
      <th>8</th>
      <th>9</th>
      <th>Runs</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <th>
        <div id="team-cell-container">
          Milwaukee Brewers
          <div class="dropdown">
            <i class="fa fa-cog" type="button" id="dropdown-item" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"></i>
            <div class="dropdown-menu" aria-labelledby="dropdown-item">
              <a class="dropdown-item" href="#">Action</a>
              <a class="dropdown-item" href="#">Another action</a>
              <a class="dropdown-item" href="#">Something else here</a>
            </div>
          </div>
        </div>
      </th>
      <td>2</td>
      <td>1</td>
      <td>4</td>
      <td>0</td>
      <td>3</td>
      <td>1</td>
      <td>1</td>
      <td>0</td>
      <td>1</td>
      <td>13</td>
    </tr>
    <tr>
      <th>Los Angles Dodgers</th>
      <td>4</td>
      <td>2</td>
      <td>0</td>
      <td>0</td>
      <td>3</td>
      <td>2</td>
      <td>4</td>
      <td>2</td>
      <td>3</td>
      <td>20</td>
    </tr>
    <tr>
      <th>New York Mets</th>
      <td>0</td>
      <td>1</td>
      <td>2</td>
      <td>0</td>
      <td>0</td>
      <td>2</td>
      <td>4</td>
      <td>0</td>
      <td>3</td>
      <td>12</td>
    </tr>
    <tr>
      <th>St. Louis Cardinals</th>
      <td>3</td>
      <td>4</td>
      <td>1</td>
      <td>3</td>
      <td>2</td>
      <td>4</td>
      <td>3</td>
      <td>2</td>
      <td>3</td>
      <td>25</td>
    </tr>
    <tr>
      <th>Houston Astros</th>
      <td>3</td>
      <td>2</td>
      <td>1</td>
      <td>4</td>
      <td>2</td>
      <td>3</td>
      <td>1</td>
      <td>3</td>
      <td>1</td>
      <td>20</td>
    </tr>
    <tr>
      <th>Toronto Blue Jays</th>
      <td>2</td>
      <td>4</td>
      <td>4</td>
      <td>1</td>
      <td>1</td>
      <td>2</td>
      <td>3</td>
      <td>4</td>
      <td>1</td>
      <td>22</td>
    </tr>
    <tr>
      <th>Boston Red Sox</th>
      <td>4</td>
      <td>4</td>
      <td>4</td>
      <td>0</td>
      <td>3</td>
      <td>0</td>
      <td>0</td>
      <td>1</td>
      <td>1</td>
      <td>17</td>
    </tr>
    <tr>
      <th>Chicago Cubs</th>
      <td>1</td>
      <td>1</td>
      <td>0</td>
      <td>0</td>
      <td>2</td>
      <td>2</td>
      <td>2</td>
      <td>0</td>
      <td>4</td>
      <td>12</td>
    </tr>
    <tr>
      <th>Philadelphia Phillies</th>
      <td>0</td>
      <td>4</td>
      <td>2</td>
      <td>0</td>
      <td>4</td>
      <td>1</td>
      <td>0</td>
      <td>4</td>
      <td>2</td>
      <td>17</td>
    </tr>
    <tr>
      <th>Chicago White Sox</th>
      <td>2</td>
      <td>0</td>
      <td>2</td>
      <td>3</td>
      <td>4</td>
      <td>2</td>
      <td>4</td>
      <td>2</td>
      <td>0</td>
      <td>19</td>
    </tr>
    <tr>
      <th>San Diego Padres</th>
      <td>2</td>
      <td>2</td>
      <td>3</td>
      <td>0</td>
      <td>4</td>
      <td>2</td>
      <td>2</td>
      <td>0</td>
      <td>2</td>
      <td>17</td>
    </tr>
    <tr>
      <th>Cleveland Indians</th>
      <td>1</td>
      <td>0</td>
      <td>0</td>
      <td>3</td>
      <td>2</td>
      <td>1</td>
      <td>3</td>
      <td>1</td>
      <td>0</td>
      <td>11</td>
    </tr>
    <tr>
      <th>San Francisco Giants</th>
      <td>1</td>
      <td>3</td>
      <td>1</td>
      <td>4</td>
      <td>1</td>
      <td>1</td>
      <td>1</td>
      <td>2</td>
      <td>3</td>
      <td>17</td>
    </tr>
    <tr>
      <th>Cincinatti Reds</th>
      <td>2</td>
      <td>2</td>
      <td>4</td>
      <td>1</td>
      <td>4</td>
      <td>2</td>
      <td>2</td>
      <td>3</td>
      <td>3</td>
      <td>23</td>
    </tr>
    <tr>
      <th>Minnesota Twins</th>
      <td>4</td>
      <td>4</td>
      <td>1</td>
      <td>0</td>
      <td>2</td>
      <td>0</td>
      <td>3</td>
      <td>1</td>
      <td>3</td>
      <td>18</td>
    </tr>
    <tr>
      <th>Tampa Bay Rays</th>
      <td>4</td>
      <td>1</td>
      <td>3</td>
      <td>0</td>
      <td>2</td>
      <td>1</td>
      <td>4</td>
      <td>0</td>
      <td>1</td>
      <td>16</td>
    </tr>
    <tr>
      <th>Miami Marlins</th>
      <td>0</td>
      <td>3</td>
      <td>0</td>
      <td>4</td>
      <td>3</td>
      <td>3</td>
      <td>0</td>
      <td>1</td>
      <td>4</td>
      <td>18</td>
    </tr>
    <tr>
      <th>Oakland Athletics</th>
      <td>3</td>
      <td>3</td>
      <td>2</td>
      <td>0</td>
      <td>4</td>
      <td>2</td>
      <td>0</td>
      <td>1</td>
      <td>0</td>
      <td>15</td>
    </tr>
    <tr>
      <th>Detroit Tigers</th>
      <td>3</td>
      <td>4</td>
      <td>1</td>
      <td>2</td>
      <td>3</td>
      <td>2</td>
      <td>0</td>
      <td>0</td>
      <td>4</td>
      <td>19</td>
    </tr>
    <tr>
      <th>Pittsburgh Pirates</th>
      <td>2</td>
      <td>2</td>
      <td>0</td>
      <td>3</td>
      <td>0</td>
      <td>2</td>
      <td>2</td>
      <td>2</td>
      <td>2</td>
      <td>15</td>
    </tr>
    <tr>
      <th>Seattle Mariners</th>
      <td>1</td>
      <td>3</td>
      <td>3</td>
      <td>1</td>
      <td>2</td>
      <td>2</td>
      <td>0</td>
      <td>4</td>
      <td>0</td>
      <td>16</td>
    </tr>
    <tr>
      <th>Atlanta Braves</th>
      <td>4</td>
      <td>3</td>
      <td>0</td>
      <td>3</td>
      <td>4</td>
      <td>4</td>
      <td>4</td>
      <td>4</td>
      <td>3</td>
      <td>29</td>
    </tr>
  </tbody>
</table>
</div>

Then use Bootstrap dropdown events to listen on show or hide the dropdown element.

$('#my-table .dropdown').on('show.bs.dropdown', (event) => {
    let thisTable = event.target.closest('table');
    thisTable.classList.add('dropdowns-opened');
    // add class to all <tr>
    $(thisTable).find('tr').addClass('non-dropdown');
    // remove class of this <tr>
    event.target.closest('tr').classList.remove('non-dropdown');
});

$('#my-table .dropdown').on('hidden.bs.dropdown', (event) => {
    let thisTable = event.target.closest('table');
    thisTable.classList.remove('dropdowns-opened');
    $(thisTable).find('tr').removeClass('non-dropdown');
});

The JavaScript above will add and remove class when dropdown element show or hide.

Now, add some CSS class to make dropdown appears on top of other.

table.dropdowns-opened tbody tr.non-dropdown th {
    z-index: 0;
}

See it in action on JsFiddle .

You maybe change your current z-index: 1 to 2 and use the class above from z-index: 0 to 1 if the sticky functional is not work as expected.