### Things I have tried

#### Without div tag:

Let $f(x)$ be continuous on $[a,\infty)$. We define $\displaystyle\int_{a}^{\infty} f(x), dx$ to be $\displaystyle\lim\limits_{t\rightarrow \infty} \int_{a}^{t} f(x), dx$.

#### With div tag:

Definition of Improper Integral
Let $f(x)$ be continuous on $[a,\infty)$. We define $\displaystyle\int_{a}^{\infty} f(x)\, dx$ to be $\displaystyle\lim\limits_{t\rightarrow \infty} \int_{a}^{t} f(x)\, dx$.

### What I’m trying to do

I attempted to surround my text with a HTML div tag. I then want to use CSS to add borders, etc. However, inside a div tag, the LaTeX is not processed.