Give this a shot:
#site-navigation .inside-navigation:before,
#site-navigation .inside-navigation:after{
position:absolute;
content: '';
display: block;
}
#site-navigation .inside-navigation:before{
width: 0.469em;
height: 100%;
padding: 0 0 0.438em;
top:0;
left: -0.469em;
background:inherit;
border-radius: 0.313em 0 0 0.313em;
visibility: visible;
overflow: visible;
line-height: 1;
font-size: inherit;
}
#site-navigation .inside-navigation:after{
width: 0.313em;
height: 0.313em;
background: rgba(0,0,0,0.35);
bottom: -0.313em;
left: -0.313em;
border-radius: 0.313em 0 0 0.313em;
box-shadow: inset -1px 2px 2px rgba(0,0,0,0.3);
visibility: visible;
overflow: visible;
line-height: 1;
font-size: inherit;
}
#site-navigation .inside-navigation {
position:relative;
padding: 0 0.5em;
font-size: 2em;
border-radius: 0 0.156em 0.156em 0;
background: rgb(123, 159, 199);
box-shadow: -1px 2px 3px rgba(0,0,0,0.5);
background: #e1662f;
height: 45px;
}
#site-navigation {
background: transparent;
}