请问下如何用css实现以下按钮选中后的效果

Question

也不一定得是按钮，这本身是一个方形div

Answer 1

.wrapper{
    position: relative;
}
.wrapper::before{
    content: "\2713";
    position: absolute;
    right: 0;
    bottom: 0;
    z-index: 100;
    color: #72a9ed;
    font-size: 20px;
    height: 20px;
    line-height: 20px;
}
.wrapper::after{
    content: '';
    position: absolute;
    right: 0;
    z-index: 10;
    width: 0;
    height: 0;
    bottom: 0;
    border-right: 15px solid #fff;
    border-top: 10px solid transparent;
    border-left: 15px solid transparent;
    border-bottom: 10px solid #fff;
}

Answer 2

背景图设成这样