Make my 2011 theme responsive – Please

I need to make this website responsive: https://www.languageconceptsllc.com/ It was done back in 2011 and it isn’t a child theme. It looks like to me the original designer edited directly into the code.

I found a thread from 3 years ago where a guy wanted his 2011 theme NOT to be responsive so he was told to remove this:

#page {
	margin: 2em auto;
	max-width: 1000px;
}

and change it to

#page {
	margin: 2em auto;
	width: 1000px;
}

On the website where I need help, I found this code in the style.css:

#page {
	margin: 0em auto 75px;
	width: 993px;
	overflow-y: hidden;
	min-height: 800px;
}

and changed it to:

#page {
	margin: 2em auto;
	max-width: 1000px;
}

And it worked.. kind-of. Some content and areas on the home page became responsive but others did not. I am hoping you can help me figure out what else needs to be changed. For this is beyond my knowledge base.

Thank you a head of time-