how to write "bold typeface" and "italics" in latex?

Question

Note: I am using jupyter notebook (MathJax) rather than tex.

"Ian Goodfellow, Yoshua Bengio, Aaron Courville. Deep Learning" use italics typeface to denote Scalars, pointed out by red arrow in the following figure

bold typeface to denote Vectors, pointed out by blue arrow in the following figure

how to write these 2 types of linear algebra notations in latex?

I searched "bold" on the author's github and got this

which is not helpful.

I tried this command

$x$ $\boldsymbol x$

which is even worse.

this command does better

$x \mathbf{x}$

although this is obviously using different font in the Deep Learning Book