<!DOCTYPE html> <html> <title>background-position-x animation overridden by important style</title> <style> @keyframes holdBackgroundPosition { from,to { background-position-x: 50%; } } #test { height: 100px; width: 100px; background-repeat: no-repeat; background-image:url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABkAAAAZCAMAAADzN3VRAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAAAZQTFRF/wAAAAAAQaMSAwAAABJJREFUeNpiYBgFo2AwAIAAAwACigABtnCV2AAAAABJRU5ErkJggg==); /* a 25x25 px red box */ background-position-x: 50% !important; animation: holdBackgroundPosition 100s infinite; } </style> <div id="test" class="reftest-opaque-layer"></div>