A user style to make JIRA boards look a lot like Trello

jirello.user.css

/* v1.0.3 */

@namespace url(http://www.w3.org/1999/xhtml);

@-moz-document domain("atlassian.net") {

  /* Backlog Ticket Preview */ 
  #ghx-detail-view {
    width: 0 !important;
  }
  
  .ghx-detail-contents {
    position: absolute;
    z-index: 100;
    top: -40px;
    left: 50%;
    margin: 0 0 0 calc(-45vw - 27px);
    width: 90vw !important;
    height: 90vh !important;
    outline: 100vw solid rgba(0, 0, 0, 0.6);
  }
  
  .ghx-header-compact .ghx-detail-contents {
    top: 5%;
  }

  /* close button */
  .ghx-detail-close .ghx-iconfont.aui-icon-small {
    color: rgba(0, 0, 0, .3);
  }
  
  .ghx-detail-close .ghx-iconfont.aui-icon-small:hover,
  .ghx-detail-close .ghx-iconfont.aui-icon-small:focus {
    color: rgba(0, 0, 0, .6);
  }
  
  .ghx-detail-close .ghx-iconfont.aui-icon-small::before {
    font-size: 22px !important;
    margin: -23px 0 0 -26px;
    padding: 11px 15px 3px;
  }
  
  .ghx-agile .aui-button.aui-button-compact {
    margin: 0 25px 0 0;
  }
  
  /* Board - Highlight my tickets */
  .ghx-issue {
    overflow: hidden;
    cursor: pointer;
  }
  
  .ghx-issue:hover {
    background: #edeff0;
  }
  
  .ghx-issue.ui-sortable-helper {
    cursor: grabbing;
    background: red;
  }
  
  /*.ghx-avatar img[alt = 'Assignee: John Doe'] {*/
  /*  outline: 350px solid rgba(0, 255, 0, .2);*/
  /*}*/
  
  /* Board - Make it look like Trello */
  .ghx-column-headers,
  #ghx-pool,
  .ghx-columns {
    background: #0079BF; /* Trello blue */
  }
  
  .ghx-swimlane:last-of-type {
    margin-top: -5px;
  }
 
  .ghx-column-headers .ghx-column,
  .ghx-columns .ghx-column {
    padding: 8px;
    background: #E3E3E3;
    border-radius: 3px;
    border-top-left-radius: 0;
    border-top-right-radius: 0;
  }
  
  .ghx-column-headers .ghx-column {
    border-bottom: 0;
    border-radius: 3px;
    border-bottom-left-radius: 0;
    border-bottom-right-radius: 0;
  }
  
  .ghx-column-headers h2 {
    float: left;
    font-size: 14px;
    line-height: 18px;
    font-weight: bold;
  }
  
  .ghx-column-headers .ghx-qty {
    position: absolute;
    top: 9px;
    right: 8px;
    margin: 0;
    font-weight: 400;
    font-size: 12px;
  }
  
  .ghx-issue {
    margin: 0 0 6px;
    border-width: 0 0 1px;
    border-radius: 3px;
  }
  
  .ghx-column > .ghx-issue:last-child {
    margin: 0;
  }
  
  .ghx-issue .ghx-avatar {
    top: auto;
    bottom: 6px;
    right: 6px;
  }
  
  .ghx-avatar-img {
    width: 30px;
    height: 30px;
  }
  
  .ghx-issue .ghx-issue-content {
    padding: 8px 10px 10px 28px;
    font: 14px "Helvetica Neue", Arial, Helvetica, sans-serif !important;
    color: #4d4d4d;
  }
  
  .ghx-issue.ghx-has-avatar .ghx-issue-fields,
  .ghx-issue.ghx-has-corner .ghx-issue-fields {
    padding-right: 31px;
  }
  
  .ghx-issue .ghx-type {
    top: 6px;
    left: 6px;
  }
  
  .ghx-issue .ghx-type,
  .ghx-issue .ghx-type img,
  .ghx-issue .ghx-flags,
  .ghx-issue .ghx-priority,
  .ghx-issue .ghx-priority img {
    overflow: visible;
    width: 12px;
    height: 12px;
  }
  
  .ghx-issue-fields .ghx-summary .ghx-inner {
    max-height: none;
  }
  
  .ghx-issue .ghx-flags {
    left: 6px;
  }
  
  #ghx-column-header-group.ghx-fixed {
    background: none;
  }
  
}