morris.js/less/morris.core.less

.morris-hover {
  position: absolute;
  z-index: 1000;

  &.morris-default-style {
    border-radius: 10px;
    padding: 6px;
    color: #666;
    background: rgba(255, 255, 255, 0.8);
    border: solid 2px rgba(230, 230, 230, 0.8);

    font-family: sans-serif;
    font-size: 12px;
    text-align: center;

    .morris-hover-row-label {
      font-weight: bold;
      margin: 0.25em 0;
    }

    .morris-hover-point {
      white-space: nowrap;
      margin: 0.1em 0;
    }
  }

}