css右上角封页角

    <div class="box">
      <div class="box-con">
        <div class="box-text">昨日</div>
      </div>
    </div>?

  .box {
    width: 180px;
    height: 100px;
    background: white;
    border-radius: 10px;
    -webkit-box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    -moz-box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    box-shadow: 0px 0px 8px rgba(0, 0, 0, 0.3);
    position: relative;
    z-index: 90;
  }
  .box .box-con{
    width: 85px;
    height: 88px;
    overflow: hidden;
    position: absolute;
    top: -3px;
    right: -3px;
  }
  .box .box-text {
    color: white;
    text-align: center;
    -webkit-transform: rotate(45deg);
    -moz-transform: rotate(45deg);
    -ms-transform: rotate(45deg);
    -o-transform: rotate(45deg);
    position: relative;
    padding: 2px 0;
    left: 35px;
    top: 10px;
    width: 65px;
    background-color: #00801C;
    background-image: -webkit-gradient(linear, left top, left bottom, from(#BFDC7A), to(#8EBF45));
    background-image: -webkit-linear-gradient(top, #BFDC7A, #8EBF45);
    background-image: -moz-linear-gradient(top, #BFDC7A, #8EBF45);
    background-image: -ms-linear-gradient(top, #BFDC7A, #8EBF45);
    background-image: -o-linear-gradient(top, #BFDC7A, #8EBF45);
    -webkit-box-shadow: 0px 0px 3px rgba(0, 0, 0, 0.3);
    -moz-box-shadow: 0px 0px 3px rgba(0, 0, 0, 0.3);
    box-shadow: 0px 0px 3px rgba(0, 0, 0, 0.3);
  }
  .box .box-text:before, .box-text:after {
    content: "";
    position: absolute;
    bottom: -3px;
  }
  .box .box-text:before {
    left: 0;
  }
  .box .box-text:after {
    right: 0;
  }