reduce width of article in a wide format without sidebar

Hi

1. Container width is 1300
2. On single post no sidebar

Reading article is difficult with long lines.

How to reduce the article width on single page ?

Trying this, but no help

@media (min-width: 700px){
	.single .one-container:not(.page) .inside-article, .single .one-container:not(.page) .comments-area {
    	padding: 0 15% 30px 15%;
	}
}

Please guide