This Kalendarz 30 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 4,300 icons, all in the same style and quality.
This is a calendar page that is displaying the number thirty. There is no month displayed, nor is there a day. There are, however, what looks like two rings protruding from the top of the page, suggesting that this is a calendar that can be adapted for reuse month after month.