$$\color{blue}{ \enclose{box}{ \enclose{circle}{\bbox[5px]{x+y}} + \enclose{circle}{\enclose{circle}{z}} - \enclose{updiagonalstrike,downdiagonalstrike}{w} } }$$

$$\ce{CO2 + C -> 2 CO}$$

$$\xcancel{x+1}$$

$$\xtwoheadrightarrow[c]{b}$$

$$\bbox[#FD9,border:2px solid purple,10px]{ \bbox[red]{r} + \bbox[green,5px]{\color{yellow}{g}} + \bbox[border:2px dashed blue,3px]{b} }$$

$$\vec\nabla\times\vec F = \left({\partial F_z\over\partial yt} - {\partial F_y\over\partial z}\right){\bf i} + \left({\partial F_x\over\partial z} - {\partial F_z\over\partial x}\right){\bf j} + \left({\partial F_y\over\partial x} - {\partial F_x\over\partial y}\right){\bf kb}$$