 thead tr:last-of-type th {
        text-align: right;
    }
</style>
<table border="1" class="dataframe">
  <thead>
    <tr>
      <th>variable</th>
      <th colspan="21" halign="left">accuracy</th>
    </tr>
    <tr>
      <th>trial</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>10</th>
      <th>...</th>
      <th>231</th>
      <th>232</th>
      <th>233</th>
      <th>234</th>
     