JSFiddle - React, Tailwind, and code Playground

HTML

<table>
  <tr>
    <th>Bryst/Biceps/Mave</th>
    <th>Gentagelser</th>
    <th>Kg</th>
  </tr>
  <tr>
    <td>Opvarmning</td>
    <td>¤</td>
    <td>¤</td>
  </tr>
  <tr>
    <td>Bænk-pres</td>
    <td>4x8-12</td>
    <td>¤</td>
  </tr>
  <tr>
    <td>Incline-Dumbbell-Pres</td>
    <td>3x10¤</td>
    <td>¤</td>
  </tr>
</table>

<br /><br /><button>Tilføj ny</button>

CSS

table, th, td {
    border: 1px solid black;
    border-collapse: collapse;
}
th, td {
    padding: 5px;
    text-align: left;    
}

th, td {
    width: 150px;
}
td:nth-child(2) {
    text-align: center;
}
tr:not(:first-child):nth-child(even){
    background: #e2efd9;
}

JavaScript

$("button").on("click", function() {
	$("table").append("<tr><td><input type='text' placeholder='Øvelse' /></td><td><input type='text' placeholder='Gentagelser' /></td><td><input type='text' placeholder='Vægt' /></td></tr>");
});