<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xHtml1-transitional.dtd">
<html XMLns="http://www.w3.org/1999/xHtml">
<head>
<meta http-equiv="Content-Type" content="text/Html; charset=utf-8" />
<title>圖片遮罩效果webjx.com</title>
<style type="text/CSS">
.trans {
-webkit-transition: 0.3s ease;
-moz-transition: 0.3s ease;
-ms-transition: 0.3s ease;
-o-transition: 0.3s ease;
transition: 0.3s ease;
}
.test_outer {
display: block;
width: 200px;
height: 200px;
margin: 1em auto;
position: relative;
overflow: hidden;
}
.test_cover {
width: 40px;
height: 40px;
border: 200px solid rgba(0, 0, 0, .35);
border-radius: 50%;
position: absolute;
left: -115px;
top: -165px;
}
.test_cover:hover {
width: 140px;
height: 140px;
left: -170px;
top: -165px;
}
.test_cover:hover:after {
content: "秋思-一葉知秋！";
text-align:center;
margin:55px 0 0 12px;
color: #fff;
font: bold 16px/1.2 '微軟雅黑';
text-shadow: 1px 1px rgba(0, 0, 0, .35);
position: absolute;
}
</style>
</head>
<body>
<a href="#" class="test_outer">
<span class="test_cover trans"></span>
<img src="這裡放一個圖片的地址" width="200" height="200" />
</a>
</body>
</Html>
其實現原理是利用個border偌大的半透明邊框屬性（demo中邊框寬度200像素），邊框顏色為rgba黑色半透明，然後50%圓角。再用用定位把它覆蓋在圖片上面。
主要核心代碼:
.test_cover {
width: 40px;
height: 40px;
border: 200px solid rgba(0, 0, 0, .35);
border-radius: 50%;
position: absolute;
left: -115px;
top: -165px;
}
然後外面再用個父容器把它溢出隱藏掉就可以了
.test_outer {
display: block;
width: 200px;
height: 200px;
margin: 1em auto;
position: relative;
overflow: hidden;
}
就這麼簡單....