<!-- inspired by the image from https://webdesign.tutsplus.com/tutorials/htmlcss-tutorials/build-an-html-email-template-from-scratch/ -->
<div class="envelope">
<div class="paper"></div>
</div>
body {
background: #70bbd9;
padding: 50px;
}
.envelope {
position: relative;
margin: 50px auto 0;
width: 98px;
height: 66px;
background: #c94548;
border-radius: 0 0 5px 5px;
box-shadow: 0 0 1px #c94548 inset;
}
.envelope:before,
.envelope:after {
content: '';
position: absolute;
width: 0;
height: 0;
border: 0 solid transparent;
border-width: 33px 49px;
}
.envelope:before {
border-bottom-color: #c94548;
top: -100%;
left: 0px;
}
.envelope:after {
border-right-color: #ed4c50;
border-left-color: #fa565a;
border-bottom-color: #fa565a;
top: 0;
border-radius: 0 0 5px 5px;
box-shadow: 0 1px 1px rgba(0,0,0,0.25);
}
.paper {
background: #fff;
width: 87px;
height: 66px;
margin: 0 auto;
border-radius: 5px;
position: absolute;
left: 6px;
top: -33px;
box-shadow: 0 1px 1px rgba(0,0,0,0.25);
}
.paper:before,
.paper:after {
content: '';
position: absolute;
left: 12px;
background: #e3f1fc;
height: 4px;
border-radius: 5px;
}
.paper:before {
top: 14px;
width: 31px;
}
.paper:after {
right: 12px;
top: 28px;
box-shadow:
0 8px 0 #e3f1fc,
0 16px 0 #e3f1fc,
0 24px 0 #e3f1fc,
0 40px 0 #e3f1fc;
}
This Pen doesn't use any external CSS resources.