ブロック要素を左右に配置

html

.content
  .header.clearfix
    %h2 詳細
    = link_to 'ダウンロード', 'https://test.com', class: 'btn btn-primary'

css

.content {
  .header {
    position: relative;
    h2 {
      float: left;
    }
    a {
      float: right;
      position: absolute;
      top: 0;
      bottom: 0;
      width: 110px;
      height: 34px;
      right: 0;
      margin-top: auto;
      margin-bottom: auto;
      margin-right: 0;
      display: block
    }
    &.clearfix:after{
      content: "";
      clear: both;
      display: block;
    }
  }
}