MathJax equations that are too wide on mobile should become individually scrollable

**Is your feature request related to a problem? Please describe.**
A longer equation like

$$
\phi_n(\kappa) =
\frac{1}{4\pi^2\kappa^2} \int_0^\infty
\frac{\sin(\kappa R)}{\kappa R}
\frac{\partial}{\partial R}
\left [ R^2\frac{\partial D_n(R)}
{\partial R} \right ] dR
$$

doesn't fit on the screen on a mobile device, resulting in it being cut off:

**Describe the solution you'd like**
The cut-off is of course unavoidable, but it would be nice if it was possible to horizontally scroll on the equation by tapping and moving it.

Injecting this CSS with the browser inspection tool seems to work, for example:

```css
.mathjax.code-block-wrapper {
overflow-x: scroll;
}
```

**Describe alternatives you've considered**
You can currently scroll horizontally, but then the whole page moves:

Then you can't read the surrounding context anymore.