<style>
.gray {
-webkit-filter: grayscale(100%);
-moz-filter: grayscale(100%);
-ms-filter: grayscale(100%);
-o-filter: grayscale(100%);
filter: grayscale(100%);
filter: gray;
opacity:0.7;//通过改变透明度来调节灰色的程度
}
</style>
<img width="36" src="img/back.png" class="gray">