This Ok icon is a responsive icon. This means that it's optimized for four resolutions, from tiny 16x16 until highly detailed 80x80. The style comes from the latest Microsoft Office, which makes it perfect for any Windows applications, in particular, those with ribbon toolbar control. Unlike other icon packs that have merely hundreds of icons, this monster icon pack contains 15,000 icons, all in the same style and quality.
There is a check mark, which is placed in the middle of a larger circle. The check mark looks similar to a reversed L, and is slanted so that the point where the two lines of the L meet is the lowest point. It is a standard check mark.