How to get a gray square around text without a WP plugin

Hello

I have a small problem, I am currently using the Bootstrap plugin on wordpress, to display a simple gray (square of the advertisement) which is the background color around the advertisement text, like here http://medicot.pl/sibutramina-sprzedam/ the bottsptrap plugin is used just for this, unfortunately Bootstrap plugin slowing down loading the page a little bit. Could someone tell me how to create the same effect as in the in link but other way, maybe in css? The plugin has many possibilities, but I only use it to display a gray square arround text.

It's mainly about putting the ad text on a gray background with a black border, or getting something similar. I don't know, maybe somehow in css or some other much simpler way than a plug-in can you achieve such an effect? It's not about putting a gray background just for the text, but to make it a square, also slightly outside the text, creating a square