css 边框添加四个角效果

1、html

2、CSS

.loginbody{
        border: 1px solid #21a7e1;
        box-shadow: 5px 5px 10px 10px  rgba(24,68,124,0.4);
        padding-top:20px;
        border-radius: 6px;
        position: relative;      }
      /*<a target="_blank" href="https://labishaxin.com/tag/1052.html" title="View all posts in 四个">四个</a>角框*/
      .border_corner{
        z-index: 2500;
        position: absolute;
        width: 19px;
        height: 19px;
        background: rgba(0,0,0,0);
        border: 4px solid #1fa5f1;
      }
      .border_corner_left_top{
        top: -2px;
        left: -2px;
        border-right: none;
        border-bottom: none;
        border-top-left-radius: 6px;
      }
      .border_corner_right_top{
        top: -2px;
        right: -2px;
        border-left: none;
        border-bottom: none;
        border-top-right-radius: 6px;
      }
      .border_corner_left_bottom{
        bottom: -2px;
        left: -2px;
        border-right: none;
        border-top: none;
        border-bottom-left-radius: 6px;
      }
      .border_corner_right_bottom{
        bottom: -2px;
        right: -2px;
        border-left: none;
        border-top: none;
        border-bottom-right-radius: 6px;
      }
.loginbody{
        border: 1px solid #21a7e1;
        box-shadow: 5px 5px 10px 10px  rgba(24,68,124,0.4);
        padding-top:20px;
        border-radius: 6px;
        position: relative;      }
      /*<a target="_blank" href="https://labishaxin.com/tag/1052.html" title="View all posts in 四个">四个</a>角框*/
      .border_corner{
        z-index: 2500;
        position: absolute;
        width: 19px;
        height: 19px;
        background: rgba(0,0,0,0);
        border: 4px solid #1fa5f1;
      }
      .border_corner_left_top{
        top: -2px;
        left: -2px;
        border-right: none;
        border-bottom: none;
        border-top-left-radius: 6px;
      }
      .border_corner_right_top{
        top: -2px;
        right: -2px;
        border-left: none;
        border-bottom: none;
        border-top-right-radius: 6px;
      }
      .border_corner_left_bottom{
        bottom: -2px;
        left: -2px;
        border-right: none;
        border-top: none;
        border-bottom-left-radius: 6px;
      }
      .border_corner_right_bottom{
        bottom: -2px;
        right: -2px;
        border-left: none;
        border-top: none;
        border-bottom-right-radius: 6px;
      }
.loginbody{
        border: 1px solid #21a7e1;
        box-shadow: 5px 5px 10px 10px  rgba(24,68,124,0.4);
        padding-top:20px;
        border-radius: 6px;
        position: relative;      }
      /*四个角框*/
      .border_corner{
        z-index: 2500;
        position: absolute;
        width: 19px;
        height: 19px;
        background: rgba(0,0,0,0);
        border: 4px solid #1fa5f1;
      }
      .border_corner_left_top{
        top: -2px;
        left: -2px;
        border-right: none;
        border-bottom: none;
        border-top-left-radius: 6px;
      }
      .border_corner_right_top{
        top: -2px;
        right: -2px;
        border-left: none;
        border-bottom: none;
        border-top-right-radius: 6px;
      }
      .border_corner_left_bottom{
        bottom: -2px;
        left: -2px;
        border-right: none;
        border-top: none;
        border-bottom-left-radius: 6px;
      }
      .border_corner_right_bottom{
        bottom: -2px;
        right: -2px;
        border-left: none;
        border-top: none;
        border-bottom-right-radius: 6px;
      }