<div class="tabs">
		<div class="tab"></div>
		<div class="tab-panel"></div>
</div>

body {
  width: 100vw;
  padding: 2vw;
  box-sizing: border-box;
  display: flex;
  justify-content: center;
}
.tabs{
			position:relative;
}
		
.tab{
			background:#336;
			width:8em;
			height:3em;
			
			position:absolute;
			left:1em;
			top:0;
			z-index:100;
			clip:rect(-10px 9em 3em -10px);
			
			box-shadow:0 0 10px #002;
      border-radius: 4px 4px 0 0;
	}
		
.tab-panel{
			background:#336;
			width:18em;
			height:20em;
			
			position:relative;
			top:3em;
			z-index:0;
			
			box-shadow:0 0 10px #002;
      border-radius: 4px;
}