仅为顶部和底部边缘创建线性渐变边框？

Question

使用下面的代码，我只能为元素的底部边缘生成线性渐变border-image。如何修改代码以使其也成为其顶部？

div {
    /* gradient shining border */
    border-style: solid;
    border-width: 3px;
    -webkit-border-image: -webkit-linear-gradient(
        left,
        rgba(0,0,0,1) 1%,
        rgba(0,255,255,1) 50%,
        rgba(0,0,0,1) 100%
    ) 0 0 100% 0/0 0 3px 0 stretch;
    -moz-border-image: -moz-linear-gradient(
        left,
        rgba(0,0,0,1) 1%,
        rgba(0,255,255,1) 50%,
        rgba(0,0,0,1) 100%
    ) 0 0 100% 0/0 0 3px 0 stretch;
    -o-border-image: -o-linear-gradient(
        left,
        rgba(0,0,0,1) 1%,
        rgba(0,255,255,1) 50%,
        rgba(0,0,0,1) 100%
    ) 0 0 100% 0/0 0 3px 0 stretch;
    border-image: linear-gradient(
        to left,
        rgba(0,0,0,1) 1%,
        rgba(0,255,255,1) 50%,
        rgba(0,0,0,1) 100%
    ) 0 0 100% 0/0 0 3px 0 stretch;
}

电流输出：

Answer 1

您正在使用简写border-image 属性来设置渐变的大小，并且根据提供的值，顶部、左侧和右侧的边框无效。

将100% 设置为顶部边框渐变的宽度并将3px 设置为其高度将导致渐变仅应用于顶部和底部。

border-image: linear-gradient(to left, rgba(0, 0, 0, 1) 1%, rgba(0, 255, 255, 1) 50%, rgba(0, 0, 0, 1) 100%) 
              100% 0 100% 0/3px 0 3px 0 stretch;

在上面的代码行中，100% 0 100% 0/3px 0 3px 0 代表渐变边框每边的大小（读作[top] [right] [bottom] [left]）。原来是0 0 100% 0/0 0 3px 0。

div {
  /* gradient shining border */
  border-style: solid;
  border-width: 3px;
  border-image: linear-gradient(to left, rgba(0, 0, 0, 1) 1%, rgba(0, 255, 255, 1) 50%, rgba(0, 0, 0, 1) 100%) 
                100% 0 100% 0/3px 0 3px 0 stretch;
  
  /* other demo stuff */
  height: 50px;
  line-height: 50px;
  background-color: #222;
  color: white;
  text-align: center;  
}

<div>Some content</div>

---

请注意border-image property still has pretty low browser support 和如果您需要支持 IE10 及更低版本将不起作用。取而代之的是，您可以像下面的 sn-p 一样使用background-image 来产生类似的效果。这在 IE10 中也有效（但在 IE9 中仍然无效——因为它们根本不支持渐变）。

div {
  /* gradient shining border */
  background-image: linear-gradient(to left, rgba(0, 0, 0, 1) 1%, rgba(0, 255, 255, 1) 50%, rgba(0, 0, 0, 1) 100%), 
                    linear-gradient(to left, rgba(0, 0, 0, 1) 1%, rgba(0, 255, 255, 1) 50%, rgba(0, 0, 0, 1) 100%);
  background-size: 100% 3px;
  background-position: 0% 0%, 0% 100%;
  background-repeat: no-repeat;
  
  /* other demo stuff */
  height: 50px;
  line-height: 50px;
  background-color: #222;
  color: white;
  text-align: center;
}

<div>Some content</div>