[html] Make content horizontally scroll inside a div

@marcio-junior's answer (https://stackoverflow.com/a/6497462/4038790) works perfectly, but I wanted to explain for those who don't understand why it works:

@a7omiton Along with @psyren89's response to your question

Think of the outer div as a movie screen and the inner div as the setting in which the characters move around. If you were viewing the setting in person, that is without a screen around it, you would be able to see all of the characters at once assuming your eyes have a large enough field of vision. That would mean the setting wouldn't have to scroll (move left to right) in order for you to see more of it and so it would stay still.

However, you are not at the setting in person, you are viewing it from your computer screen which has a width of 500px while the setting has a width of 1000px. Thus, you will need to scroll (move left to right) the setting in order to see more of the characters inside of it.

I hope that helps anyone who was lost on the principle.