border 테두리에 삼각형 그리기

.checked::after {
 content: '';
 position: absolute;
 width: 0;
 height: 0;
 top: 0;
 right: 0;
 border-top: 10px solid #b4b4b4;
 border-right: 10px solid #b4b4b4;
 border-left: 10px solid transparent;
 border-bottom: 10px solid transparent;
}