.container {
display:inline-block;
width:25%;
height:25%;
padding:1.5em;
background: rgb(123,215,193);
background: linear-gradient(90deg, rgba(123,215,193,1) 4%, rgba(225,233,148,1) 97%);
}
.key {
height: 3em;
width: 3em;
}
.grey-out {
opacity: 0.4;
-webkit-filter: grayscale(100%);
filter: grayscale(100%);
}
.hue-rotate {
-webkit-filter: hue-rotate(90deg);
filter: hue-rotate(90deg);
}
.invert {
-webkit-filter: invert(100%);
filter: invert(100%);
}
<div class="container">
<img class="key" src="https://twemoji.maxcdn.com/svg/1f511.svg">
<img class="key grey-out" src="https://twemoji.maxcdn.com/svg/1f511.svg">
<img class="key hue-rotate" src="https://twemoji.maxcdn.com/svg/1f511.svg">
<img class="key invert" src="https://twemoji.maxcdn.com/svg/1f511.svg">
</div>