Bootstrap工具提示有效但由于z-index而隐藏？

如果你将鼠标悬停在第一个铅笔上，你会看到提示框弹出，但是它是隐藏的。

如何让所有的提示框都显示在最上方？

相关代码

$('.nav-text').on('click', null, function () {
    alert('heyo');
});
$('.nav-text').tooltip({
    'placement': 'right',
        'title': 'heyo'
});

完整示例

$('.down').click(function() {
  var $move = $('.side-study-box ul');
  $move.css({
    top: '-=20px'
  })
})
$('.up').click(function() {
  var $move = $('.side-study-box ul');
  $move.css({
    top: '+=20px'
  })
})
$('.nav-text').on('click', null, function() {
  alert('heyo');
});
$('.nav-text').tooltip({
  'placement': 'right',
  'title': 'heyo'
});

.side-study-box {
  background-color: white;
  color: black;
  border: 1px solid #3D6AA2;
  text-align: center;
  height: 160px;
  display: table !important;
  margin: 0px !important;
  margin-left: -1px !important;
}
.side-study-box .viewport {
  height: 120px;
  overflow: hidden;
  position: relative;
}
.side-study-box span {
  position: relative;
  width: 100%;
  font-size: 24px;
  display: table-cell;
  vertical-align: middle;
}
.side-study-box textarea {
  position: relative;
  height: 195px;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
  width: 100%;
  margin: auto;
  font-size: 18px;
  font-family: Consolas, Monaco, Lucida Console, Liberation Mono, DejaVu Sans Mono, Bitstream Vera Sans Mono, Courier New;
  display: table-cell;
  vertical-align: middle;
  resize: none;
}
.side-study-box i {
  margin: 0px !important;
  padding-right: 1px;
}
.side-study-box .side-box-menu {
  border-right: 1px solid #335987;
  width: 28px;
  text-align: center;
  height: 100%;
}
.side-box-menu-nav {
  display: inline-block;
  cursor: pointer;
  text-decoration: none !important;
  margin: 0px;
  width: 100%;
  background-color: #3D6AA2;
  color: white;
}
.side-box-menu-nav:hover {
  background-color: #335987 !important;
  color: white !important;
}
.side-study-box ul {
  list-style-type: none;
  margin: 0px;
  margin-left: -1px !important;
  padding: 0px;
  padding-right: 2px;
  height: 100%;
  color: #335987;
  position: absolute;
  top: 0;
}
.side-study-box ul li {
  margin: 0px;
}
.side-study-box ul li :hover {
  color: black;
}
.side-study-box ul li a {
  padding-left: 3px;
  cursor: pointer;
  text-decoration: none;
  display: inline-block;
  margin: 0px;
  color: gray;
}
.side-study-box ul li a .side-box-menu-control {
  padding-top: 3px;
  height: 23px;
}