css之斜线

.x {
            border: solid 1px red;
            width: 100px;
            height: 100px;
            position: relative;
            background-color: transparent;
        }

            .x:before {
                position: absolute;
                top: 0px;
                right: 0;
                left: 0;
                bottom: 0;
                border-bottom: 100px solid red;
                border-left: 100px solid transparent;
                content: "";
            }

            .x:after {
                position: absolute;
                left: 1px;
                right: 0;
                top: 1px;
                bottom: 0;
                border-bottom: 99px solid white;
                border-left: 99px solid transparent;
                content: "";
            }

        .f {
            border: solid 1px red;
            width: 100px;
            height: 100px;
            position: relative;
            background-color: transparent;
        }

            .f:before {
                position: absolute;
                top: 0px;
                right: 0;
                left: 0;
                bottom: 0;
                border-bottom: 100px solid red;
                border-right: 100px solid transparent;
                content: "";
            }

            .f:after {
                position: absolute;
                left: 0;
                right: 1px;
                top: 1px;
                bottom: 0;
                border-bottom: 99px solid white;
                border-right: 99px solid transparent;
                content: "";
            }