background-color: светлый цвет.
color: white;
border-bottom: 1px solid #цвет
.content-inner {
width: 300px;
height:300px;
background: #FFF;
box-shadow: 0 1px 2px rgba(0,0,0,0.2);
position:relative;
}
.content-inner::before {
content: "";
display: block;
border: 11px solid transparent;
border-right-color: #DDD;
position: absolute;
top: 47px;
left: -22px;
}
.content-inner::after {
content: "";
display: block;
border: 10px solid transparent;
border-right-color: #FFF;
position: absolute;
top: 48px;
left: -20px;
}