<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  
  <h2>что выходит</h2>
  <table>
    <tr>
      <td>один</td>
      <td>два</td>
      <td>три</td>
    </tr>
    <tr>
      <td>четыре</td>
      <td>пять</td>
      <td>шесть</td>
    </tr>
    <tr>
      <td>семь</td>
      <td>восемь</td>
      <td>девять</td>
    </tr>
  </table>
  

  
</div>
</html>
table {
  background-origin: border-box;
  border-spacing: 0 5px;
}


tr {
  position:relative;
}
tr:not(:first-child):after {
  position: absolute;
  background-image: linear-gradient(90deg, red 0%, blue 100%);
  display: block;
  top: -5px;
  left: 0;
  width: 100%;
  height: 5px;
  content: "";
}

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