Комментарий shpargalkablog.ru/2012/03/css-tabs.html#c7558189358028859464

by NMitra

HTML

<div id="raz">
  <div><span>CSS</span>1 вкладка</div>
  <div><span>HTML</span>2 вкладка</div>
  <div><span>Дополнительно</span>3 вкладка</div>
</div>

CSS

#raz { /* корпус */ 
  position: relative;
  height: 250px;
  border-top: 30px solid #fff;
}
#raz > div { /* вкладка */ 
  position: absolute;
  z-index: 1;
  height: 100%;
  width: 100%;
  visibility: collapse;
  transition: 0s 9999999s;
  box-sizing: border-box;
  background: #fff;
  padding: 5px;
}
#raz > div:before { /* рамка вкладки */ 
  content: "";
  position: absolute;
  z-index: -1;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  border: #808080 solid 1px;
  border-top: none;
}
#raz > div:hover, #raz > div:nth-of-type(1) {
  visibility: visible;
  transition: 0s;
}
#raz:hover > div:not(:hover) {
  visibility: hidden;
  transition: 0s;
}
#raz > div > span { /* кнопка */ 
  position: absolute;
  top: -30px;
  line-height: 30px;
  height: 30px;
  width: 33.33%; /* 4 вкладки, а значит 100/4 */ 
  text-align: center;
  box-sizing: border-box;
  border: 1px solid rgb(128,128,128);
  border-left-color: rgba(0,0,0,0);
  visibility: visible;
  transition: 0s 9999999s;
  cursor: pointer;
}
#raz > div:nth-of-type(1) > span {left: 0; border-left-color: rgb(128,128,128);}
#raz > div:nth-of-type(2) > span {left: 33.33%;}
#raz > div:nth-of-type(3) > span {left: 66.66%;}
#raz > div:hover > span, #raz > div:nth-of-type(1) > span {
  border-bottom-color: rgba(0,0,0,0);
  transition:  0s;
}
#raz:hover > div:not(:hover) > span {
  border-bottom-color: rgba(128,128,128,.99);
  transition:  0s;
}
#raz > div:not(:nth-of-type(1)):not(:hover):after { /* появляется нижняя граница у первой кнопки */ 
  content: "";
  left: 0;
  position: absolute;
  top: -1px;
  width: 33.33%;
  border-top: 1px solid rgb(128,128,128);
}