This Add to Favorites icon is made in Material Design style developed by Google. This style is based on extremely simplified shapes, thin two-pixel lines, and is optimized for 24x24 px. Unlike other vector icon packs that have merely hundreds of icons, this icon pack contains 5,300 icons, all in the same style and quality.
There is a "plus" sign which is like a cross, but the sides are even, centered inside a five pointed star with all sides that are equal. Both are outlined in black. The star is "hollow" otherwise" in that there is empty space surrounding the icon. Everything is straight (there are no curved lines).