The Four Categories of Optional Prayers

Shaykh ‘Uthaymīn (rahimahullah):

The optional prayers are of four categories:

1.  Optional prayers whose performance are restricted by time, such as Salātul Witr.
2. Optional prayers whose performance are restricted to the obligatory (prayers), such as the Rawātib Prayers (e.g. two units before the Fajr prayer e.t.c)
3. Optional prayers whose performance are restricted due to a specific reason, such as Tahiyyatul Masjid (2 units of prayer performed before sitting in the masjid).
4. Unrestricted optional prayers, it is Sunnah to perform them at anytime, excluding the times of prohibition (e.g. when sun is setting etc).

Paraphrased from Shaykh ‘Uthaymīn’s Fath Dhīl Jalāli wal Ikrām Sharh Bulūgh al-Marām Vol.2 Pg.223

Are the 2 Rakah before Maghrib from the Sunnah?