.triangle-bottomright {
width: 1px;
height: 1px;
border-bottom: 150px solid red;
border-left: 350px solid transparent;
 margin-top: -151px;
}

.triangle-topleft {
width: 1px;
height: 1px;
border-top: 150px solid red;
border-right: 350px solid transparent;
}