Single post in Site Skins: How-To, and Helpful CSS

Try this instead. It worked for me. #header > #social > #notifs > a { background-image: url('https://vignette.wikia.nocookie.net/pkmnshuffle/images/5/55/Greninja_%28Ash-Greninja%29.png/revision/latest/thumbnail-down/width/256/height/256?cb=20170410223510'); background-size: cover; background-position: center center; background-repeat: no-repeat; } #header > #social > #notifs > a > img { opacity: 0; }