How to make a theme wide

one uses fixed width (for example width: 700px) and one uses fluid width (width: 100%;)

Any chance you could tell me where exactly do I change that? I mean, there are quite a few template files in those themes. Which one do I check for that parameter?

it would be in your style sheet. i cant be very specific unless you give me a link to your site running that theme. the themes link you posted has no demo.

https://wordpress.petrabbitlife.com/ this one is running Unsleepable theme right now. I like the theme a lot, but it’s just not as wide as I want it to be >>> https://themes.wordpress.net/columns/3-columns/3307/genkitheme-10/ So I would like to make Unsleepable as wide as GenkiTheme.

well that theme makes use of a few different background images, so you will run into a few problems. but if you wanna mess with it, you should look in your stylesheet for entries that have a set px width, like the following

#page {
	background: #f9f9f9 url('images/page_bg.gif') top center repeat-y;
	background-position: right !important;
	text-align: left;
	margin: 0px auto 0px !important;
	padding: 0 !important;
	position: relative;
	width: 785px;
	}

#primary {
	width: 500px;
	float: left;
	padding: 20px 0 10px;
	margin: 0 10px 0 30px;
	display: inline;
	}