Edit in JSFiddle

<ul class="tabs">
    <li>
        <input type="radio" name="tabs" id="tab1" checked />
        <label for="tab1">tab1</label>
        <div id="tab-content1" class="tab-content">
            <p>tab1 content</p>
        </div>
    </li>
    <li>
        <input type="radio" name="tabs" id="tab2" />
        <label for="tab2">tab2</label>
        <div id="tab-content2" class="tab-content">
            <p>tab2 content</p>
        </div>
    </li>  
    <li>
        <input type="radio" name="tabs" id="tab3" />
        <label for="tab3">tab3</label>
        <div id="tab-content3" class="tab-content">
          <p>tab3 content</p>
        </div>
    </li>
</ul>

body {
    background: #D7D3C8;
    color: #424F5A; 
    text-align: left;
}
.tabs {
    float: none;
    list-style: none;
    margin: auto;
    padding: 0;
    position: relative;
    text-align: left;
    width: 380px;
}
.tabs li {
    display: block;
    float: left;
}
.tabs input[type="radio"] {
    display: none;
    position: absolute;
}
.tabs label {
    background: #AAA;
    border-radius: 5px 5px 0 0;
    cursor: pointer;
    display: block;
    font-size: 20px;
    padding: 14px 21px;
    position: relative;
    transition: all 0.2s ease-in-out;
    top: 4px;
    width: 50px;
    -webkit-border-radius: 5px 5px 0 0;
    -webkit-transition: all 0.2s ease-in-out;
}
.tabs label:hover {
    background: #CCC;
}
.tabs .tab-content{
    background: #FFF;
    display: none; 
    font-size: 17px;
    left: 0;
    line-height: 25px;
    overflow: hidden;
    position: absolute;
    top: 52px;
    width: 100%;
    z-index: 2;
}
.tabs .tab-content p{
    padding: 0 20px;
}
.tabs [name="tabs"]:checked + label { 
    background: #FFF;
    padding-top: 17px; 
    top: 0;
}
.tabs [name="tabs"]:checked ~ .tab-content {
    display: block;
}

@media only screen and (max-width: 400px) {
  .tabs {
    width: 100%;
  }
  .tabs li {
    float: none;
    margin-top: 20px;
  }
  .tabs .tab-content {
    display: block;
    position: relative;
    top: 0;
  }
  .tabs label {
    background: #FFF;
    padding-top: 17px; 
    top: 0;
  }
  .tabs label:hover {
    background: #FFF;
  }
}