at the bottom to add svg-filter
use "+" to add a new filter and copy following code
<filter id="inset-shadow"><feOffset dx="25" dy="25"></feOffset><feGaussianBlur result="offset-blur" stdDeviation="10"></feGaussianBlur><feComposite in="SourceGraphic" in2="offset-blur" operator="out" result="inverse"></feComposite><feFlood flood-color="black" flood-opacity=".75" result="color"></feFlood><feComposite in="color" in2="inverse" operator="in" result="shadow"></feComposite><feComposite in="shadow" in2="SourceGraphic" operator="over"></feComposite></filter>