CSS-使用background实现四个角边框

使用background实现四个角边框。
CSS

.question_title_content {
    background: linear-gradient(to left, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) left top no-repeat, 
 linear-gradient(to bottom, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) left top no-repeat, 
 linear-gradient(to left, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) right top no-repeat,
 linear-gradient(to bottom, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) right top no-repeat, 
 linear-gradient(to left, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) left bottom no-repeat,
 linear-gradient(to bottom, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) left bottom no-repeat,
 linear-gradient(to left, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) right bottom no-repeat,
 linear-gradient(to left, rgba(51, 51, 51, 1), rgba(51, 51, 51, 1)) right bottom no-repeat;
   /*设置大小*/
    background-size: 0.15rem 0.6rem, 0.6rem 0.15rem, 0.15rem 0.6rem, 0.6rem 0.15rem;
}

HTML

内容

效果：