Add inner corner curved border to active menu

Question

I am trying to create an inner curved border for active/selected menu. Below snippet is so far the best I can do, the square corner shouldn't be visible. Solutions from google doesn't seem to help... Please help me play with it. Thanks guys!

FIDDLE HERE.

body {
  background:#eee;width:90%;margin:20px auto
}
ul {
  margin: 0;
  padding: 0;
}
ul li {
  display: inline-block;
  list-style: none;
  position: relative;
  vertical-align:bottom;
}
ul li a {
  padding: 10px 15px;
  display: block;
  line-height: 25px;
  margin-bottom:-1px;
}
ul li.active a {
  background:#fff;
  border:1px solid #aaa;
  border-bottom:0;
  border-radius:5px 5px 0 0;
}

ul li.active:before,
ul li.active:after {
  content:"";
  position:absolute;
  bottom:-1px;
  width:10px;
  height:10px;
  border:solid #aaa;
}
ul li.active:before {
  left:-10px;
  border-radius:8px 0;
  border-width:0 1px 1px 0
}
ul li.active:after {
  right:-10px;
  border-radius: 0 8px;
  border-width:0 0 1px 1px;
}

.content {
  border:1px solid #aaa;background:#fff;height:200px
}

<ul>
    <li><a href="#">tab 1</a></li>
    <li class="active"><a href="#">tab2</a></li>
    <li><a href="#">tab3</a></li>
    <li><a href="#">tab4</a></li>
</ul>
<div class="content"></div>

Answer 1

This is my solution so far. But I am hoping there is a better solution out there... I use the pseudo element of active a to create a white border to hide the sharp corner.

body {
  background:#eee;width:90%;margin:20px auto
}
ul {
  margin: 0;
  padding: 0;
}
ul li {
  display: inline-block;
  list-style: none;
  position: relative;
  vertical-align:bottom;
}
ul li a {
  padding: 10px 15px;
  display: block;
  line-height: 25px;
  margin-bottom:-1px;
}
ul li.active a {
  background:#fff;
  border:1px solid #aaa;
  border-bottom:0;
  border-radius:5px 5px 0 0;
}

ul li.active:before,
ul li.active:after {
  content:"";
  position:absolute;
  bottom:-1px;
  width:10px;
  height:10px;
  border:solid #aaa;
}
ul li.active:before {
  left:-10px;
  border-radius:50% 0;
  border-width:0 1px 1px 0;
  box-shadow: 1px 1px white;
}
ul li.active:after {
  right:-10px;
  border-radius: 0 50%;
  border-width:0 0 1px 1px;
  box-shadow: -1px 1px white;
}

.content {
  border:1px solid #aaa;background:#fff;height:200px
}

<ul>
    <li><a href="#">tab 1</a></li>
    <li class="active"><a href="#">tab2</a></li>
    <li><a href="#">tab3</a></li>
    <li><a href="#">tab4</a></li>
</ul>
  <div class="content"></div>

UPDATE: My previous answer requires more css so I edited it. Based on the answer of jbutler, I got the idea about adding box-shadow to hide the corners. Nothing much changed on the original css I presented here, I just added the box-shadow. Updated fiddle HERE.