trapezoid tab

trapezoid.css

/**
 * Trapezoid tabs
 */

body {
	padding: 40px;
	font: 130%/2 Frutiger LT Std, sans-serif;
}

nav {
	position: relative;
	z-index: 1;
	padding-left: 1em;
}

nav > a {
	position: relative;
	display: inline-block;
	padding: .3em 1em 0;
	color: inherit;
	text-decoration: none;
	margin: 0 -.3em;
} 

nav > a::before,
main {
	border: none;
}

nav a::before {
	content: ''; /* To generate the box */
	position: absolute;
	top: 0; right: 0; bottom: 0; left: 0;
	z-index: -1;
	border-bottom: none;
	border-radius: 0em 0em 0 0;
	background: #ccc linear-gradient(hsla(0,0%,100%,.6), hsla(0,0%,100%,0));
	box-shadow: 0 .15em white inset;
	
	border: none;	
	transform: scale(1.2, 1.3) perspective(0.5em) rotateX(5deg);
	transform-origin: bottom left;
}



main {
	display: block;
	margin-bottom: 1em;
	background: #eee;
	padding: 1em;
	border-radius: .15em;
}

nav.left > a::before {

}

<nav class="left">
    <a href="#">Home</a>
</nav>