The marker-start CSS property points to a marker that will be drawn on the first vertex of the element's path; that is, at its starting vertex. The marker must have been defined using an SVG <marker> element, and can only be referenced with a <url> value. The value of the CSS property overrides any values of the marker-start attribute in the SVG.
For many marker-supporting shapes, the first and last vertices are in the same place: for example, the top left corner of a <rect>. In such shapes, if both the first and last markers are defined, two markers will be drawn at that point, though they may not point in the same direction.
Note: The marker-start property will only have an effect for elements that can use SVG markers. See marker-start for a list.