If you want to have a different icon for each list-item, I suggest adding icons in HTML instead of using a pseudo element to keep your CSS down. It can be done quite simply as follows:
<ul>
<li><span><i class="mdi mdi-lightbulb-outline"></i></span>An electric light with a wire filament heated to such a high temperature that it glows with visible light</li>
<li><span><i class="mdi mdi-clipboard-check-outline"></i></span>A thin, rigid board with a clip at the top for holding paper in place.</li>
<li><span><i class="mdi mdi-finance"></i></span>A graphical representation of data, in which the data is represented by symbols, such as bars in a bar chart, lines in a line chart, or slices in a pie chart.</li>
<li><span><i class="mdi mdi-server"></i></span>A system that responds to requests across a computer network worldwide to provide, or help to provide, a network or data service.</li>
</ul>
-
ul {
list-style-type: none;
margin-left: 2.5em;
padding-left: 0;
}
ul>li {
position: relative;
}
span {
left: -2em;
position: absolute;
text-align: center;
width: 2em;
line-height: inherit;
}
In this case I used Material Design Icons