Is reducing the area of marble on the mosque's stairs by creating grass beds opposite the pillars, for the purpose of saving and economy, considered an innovation (bid'ah)?

This act is not an innovation; rather, it is a praiseworthy deed for which its doer will be rewarded, as it combines avoiding extravagance and waste in building mosques with beautifying and adorning them in a permissible way. This falls under the general principle of revering and maintaining mosques, which Allah has commanded, in accordance with His saying: ﴿In houses which Allah has permitted to be raised and that His name be remembered therein; therein glorified be He in the mornings and in the evenings﴾ [An-Nur:36], and in accordance with the saying of the Prophet, peace and blessings of Allah be upon him: "The Messenger of Allah, peace and blessings of Allah be upon him, commanded that mosques be built in dwellings, and that they be cleaned and perfumed." Narrated by Abu Dawud and Ibn Majah.