index.html

<style>
  @import url("rotated-header.css")
</style>
<div class="scrollable-table">
  <table class="table table-striped table-header-rotated">
    <thead>
      <tr>
        <!-- First column header is not rotated -->
        <th></th>
        <!-- Following headers are rotated -->
        <th class="column criterion rotate-45"><div><span>Column header 1</span></div></th>
        <th class="column criterion rotate-45"><div><span>Column header 2</span></div></th>
        <th class="column criterion rotate-45"><div><span>Column header 3</span></div></th>
        <th class="column criterion rotate-45"><div><span>Column header 4</span></div></th>
        <th class="column criterion rotate-45"><div><span>Column header 5</span></div></th>
        <th class="column criterion rotate-45"><div><span>Column header 6</span></div></th>
      </tr>
    </thead>
    <tbody>
      <tr>
        <th class="row-header">Row header 1</th>
        <td><input checked="checked" name="column1[]" type="radio" value="row1-column1"></td>
        <td><input checked="checked" name="column2[]" type="radio" value="row1-column2"></td>
        <td><input name="column3[]" type="radio" value="row1-column3"></td>
        <td><input name="column4[]" type="radio" value="row1-column4"></td>
        <td><input name="column5[]" type="radio" value="row1-column5"></td>
        <td><input name="column6[]" type="radio" value="row1-column6"></td>
      </tr>
      <tr>
        <th class="row-header">Row header 2</th>
        <td><input name="column1[]" type="radio" value="row2-column1"></td>
        <td><input name="column2[]" type="radio" value="row2-column2"></td>
        <td><input checked="checked" name="column3[]" type="radio" value="row2-column3"></td>
        <td><input checked="checked" name="column4[]" type="radio" value="row2-column4"></td>
        <td><input name="column5[]" type="radio" value="row2-column5"></td>
        <td><input name="column6[]" type="radio" value="row2-column6"></td>
      </tr>
      <tr>
        <th class="row-header">Row header 3</th>
        <td><input name="column1[]" type="radio" value="row3-column1"></td>
        <td><input name="column2[]" type="radio" value="row3-column2"></td>
        <td><input name="column3[]" type="radio" value="row3-column3"></td>
        <td><input name="column4[]" type="radio" value="row3-column4"></td>
        <td><input checked="checked" name="column5[]" type="radio" value="row3-column5"></td>
        <td><input checked="checked" name="column6[]" type="radio" value="row3-column6"></td>
      </tr>
    </tbody>
  </table>
</div>

rotated-header.css

.table-header-rotated th.row-header{
  width: auto;
}

.table-header-rotated td{
  width: 40px;
  border-top: 1px solid #dddddd;
  border-left: 1px solid #dddddd;
  border-right: 1px solid #dddddd;
  vertical-align: middle;
  text-align: center;
}

.table-header-rotated th.rotate-45{
  height: 80px;
  width: 40px;
  min-width: 40px;
  max-width: 40px;
  position: relative;
  vertical-align: bottom;
  padding: 0;
  font-size: 12px;
  line-height: 0.8;
}

.table-header-rotated th.rotate-45 > div{
  position: relative;
  top: 0px;
  left: 40px; /* 80 * tan(45) / 2 = 40 where 80 is the height on the cell and 45 is the transform angle*/
  height: 100%;
  -ms-transform:skew(-45deg,0deg);
  -moz-transform:skew(-45deg,0deg);
  -webkit-transform:skew(-45deg,0deg);
  -o-transform:skew(-45deg,0deg);
  transform:skew(-45deg,0deg);
  overflow: hidden;
  border-left: 1px solid #dddddd;
  border-right: 1px solid #dddddd;
  border-top: 1px solid #dddddd;
}

.table-header-rotated th.rotate-45 span {
  -ms-transform:skew(45deg,0deg) rotate(315deg);
  -moz-transform:skew(45deg,0deg) rotate(315deg);
  -webkit-transform:skew(45deg,0deg) rotate(315deg);
  -o-transform:skew(45deg,0deg) rotate(315deg);
  transform:skew(45deg,0deg) rotate(315deg);
  position: absolute;
  bottom: 30px; /* 40 cos(45) = 28 with an additional 2px margin*/
  left: -25px; /*Because it looked good, but there is probably a mathematical link here as well*/
  display: inline-block;
  width: 85px; /* 80 / cos(45) - 40 cos (45) = 85 where 80 is the height of the cell, 40 the width of the cell and 45 the transform angle*/
  text-align: left;
  /* white-space: nowrap; *//*whether to display in one line or not*/
}