我同意szajmon的观点。他和昆汀回答的唯一问题是跨浏览器兼容性。

HTML:

<div class="g">
    <div>bla</div>
</div>

CSS:

.g {
background-image: -webkit-linear-gradient(300deg, white, black, white); /* webkit browsers (Chrome & Safari) */
background-image: -moz-linear-gradient(300deg, white, black, white); /* Mozilla browsers (Firefox) */
filter: progid:DXImageTransform.Microsoft.gradient(startColorstr='#ffffff', endColorstr='#000000', gradientType='1'); /* Internet Explorer */
background-image: -o-linear-gradient(300deg,rgb(255,255,255),rgb(0,0,0) 50%,rgb(255,255,255) 100%); /* Opera */
}

.g > div { background: #fff; }

这是一个很好的半跨浏览器的方法，有渐变边界，淡出一半。只需将颜色停止设置为rgba(0,0,0,0)

.fade-out-borders {
min-height: 200px; /* for example */

-webkit-border-image: -webkit-gradient(linear, 0 0, 0 50%, from(black), to(rgba(0, 0, 0, 0))) 1 100%;
-webkit-border-image: -webkit-linear-gradient(black, rgba(0, 0, 0, 0) 50%) 1 100%;
-moz-border-image: -moz-linear-gradient(black, rgba(0, 0, 0, 0) 50%) 1 100%;
-o-border-image: -o-linear-gradient(black, rgba(0, 0, 0, 0) 50%) 1 100%;
border-image: linear-gradient(to bottom, black, rgba(0, 0, 0, 0) 50%) 1 100%;
}

<div class="fade-out-border"></div>

用法解释:

Formal grammar: linear-gradient(  [ <angle> | to <side-or-corner> ,]? <color-stop> [, <color-stop>]+ )
                              \---------------------------------/ \----------------------------/
                                Definition of the gradient line         List of color stops  

更多信息请点击:https://developer.mozilla.org/en-US/docs/Web/CSS/linear-gradient

而不是边框，我会使用背景渐变和填充。同样的外观，但更简单，更有支撑。

举个简单的例子:

.g { Background-image: -webkit-gradient(线性，左下，左上，彩色停止(0.33,rgb(14,173,173))，彩色停止(0.67,rgb(0,255,255))); 背景-图像:-moz-linear-gradient(中底，rgb(14,173,173) 33%， rgb(0,255,255) 67%); 填充:2 px; ｝ .g > div{背景:#fff;｝ < div class = " g " > < div > bla < / div > < / div >

编辑:你也可以利用:before选择器@WalterSchwarz指出:

body { padding: 20px; } .circle { width: 100%; height: 200px; background: linear-gradient(to top, #3acfd5 0%, #3a4ed5 100%); border-radius: 100%; position: relative; text-align: center; padding: 20px; box-sizing: border-box; } .circle::before { border-radius: 100%; content: ''; background-image: linear-gradient(to bottom, #3acfd5 0%, #3a4ed5 100%); top: -10px; left: -10px; bottom: -10px; right: -10px; position: absolute; z-index:-1; } <div class="circle"></div>

渐变边框来自Css-Tricks: http://css-tricks.com/examples/GradientBorder/

.multbg-top-to-bottom {
  border-top: 3px solid black;
  background-image: -webkit-gradient(linear, 0 0, 0 100%, from(#000), to(transparent));
  background-image: -webkit-linear-gradient(#000, transparent);
  background-image:
      -moz-linear-gradient(#000, transparent),
      -moz-linear-gradient(#000, transparent);
  background-image:
      -o-linear-gradient(#000, transparent),
      -o-linear-gradient(#000, transparent);
  background-image: 
      linear-gradient(#000, transparent),
      linear-gradient(#000, transparent);
  -moz-background-size: 3px 100%;
  background-size: 3px 100%;
  background-position: 0 0, 100% 0;
  background-repeat: no-repeat; 
}

这是一个hack，但是在某些情况下你可以通过使用background-image来指定渐变，然后用box-shadow掩盖实际的背景来达到这种效果。例如:

p {
  display: inline-block;
  width: 50px;
  height: 50px;
  /* The background is used to specify the border background */
  background: -moz-linear-gradient(45deg, #f00, #ff0);
  background: -webkit-linear-gradient(45deg, #f00, #ff0);
  /* Background origin is the padding box by default.
  Override to make the background cover the border as well. */
  -moz-background-origin: border;
  background-origin: border-box;
  /* A transparent border determines the width */
  border: 4px solid transparent;
  border-radius: 8px;
  box-shadow:
    inset 0 0 12px #0cc, /* Inset shadow */
    0 0 12px #0cc, /* Outset shadow */
    inset -999px 0 0 #fff; /* The background color */
}

来自:http://blog.nateps.com/the-elusive-css-border-gradient

border-image属性可以实现这一点。您还需要指定border-style和border-width。

border-image: linear-gradient(#f6b73c, #4d9f0c) 30;
border-width: 4px;
border-style: solid;

在MDN上阅读更多。