用css在缩略图顶部覆盖播放图标

Question

我试图用css在缩略图上覆盖一个播放图标，但没有成功。

<ul class="thumb-grid">
        <li class="play-icon"><img src="image.url"/></li>
</ul>

悬停时可以看到图标，但无法将图标放在缩略图的顶部。有人知道怎么做吗？

这是Fiddle

Answer 1

使用伪元素并更改position样式。

为了保持悬停效果，您可以将:hover选择器附加到列表项，并将img作为目标：

html, body {
    margin: 0;
    padding: 0;
}
.content {
    font-size: 10px;
    margin: 0 auto 0;
    width: 75%;
    max-width: 750px;
    text-align: left;
    padding-bottom: 3em;
    background-color: #eee;
}
p {
    font-size: 2em;
    line-height: 1.4em;
    letter-spacing: normal;
    font-style: normal;
    font-weight: normal;
    margin: 0 0 1em 0;
}
.play-icon:after {
    position:absolute;
    top:0;
    left:0;
    content:'';
    width: 100%;
    height: 100%;
    background: url("https://cdn1.iconfinder.com/data/icons/video-controls/32/play-20.png");
    background-repeat: no-repeat;
    background-position: center center;
    background-color: transparent;
    z-index: 9999;
}
.thumb-grid {
    display: block;
    width: 100%;
    padding: 0;
    margin: 3em 0 3em 0;
    background-color:;
    list-style-type: none;
}
.thumb-grid:after {
    content:'';
    width: 0;
    display: block;
    clear: both;
}
.thumb-grid li {
    position: relative;
    overflow: hidden;
    width: 16%;
    margin: 0 5% 5% 0;
    display: block;
    float: left;
    padding-bottom: 16%;
}
.thumb-grid li:nth-child(5n) {
    margin-right: 0;
}
.thumb-grid img {
    position: absolute;
    left: 0;
    top: 0;
    cursor: pointer;
    width: 100%;
    background-color: #ccc;
}
.thumb-grid li:hover img {
    opacity: 0.5;
}

<div class="content">
    <p>Een dynamische quiz in teams, die wordt geleid door een enthousiaste en bekwame quizmaster. Doormiddel van beeld en geluid wordt een breed scala aan vragen voorgelegd. Het raden van tunes, videofragmenten, teksten, foto’s met de hand op de quiz-knop of na teamberaad.</p>
    <ul class="thumb-grid">
        <li class="play-icon"><img src="http://images.kaneva.com/filestore9/5112880/6412551/squareUyellowUsmileyUface_ad.jpg" /></li>
        <li><img src="http://images.kaneva.com/filestore9/5112880/6412551/squareUyellowUsmileyUface_ad.jpg" /></li>
        <li><img src="http://images.kaneva.com/filestore9/5112880/6412551/squareUyellowUsmileyUface_ad.jpg" /></li>
        <li><img src="http://images.kaneva.com/filestore9/5112880/6412551/squareUyellowUsmileyUface_ad.jpg" /></li>
        <li><img src="http://images.kaneva.com/filestore9/5112880/6412551/squareUyellowUsmileyUface_ad.jpg" /></li>
    </ul>
</div>