The CSS class screen-reader-text is a WordPress Generated Class. Each theme should have these styles in its CSS.
The :focus style is primarily used by skip links. The colors, borders and padding of the focus style can be adjusted to match the styling of the theme. The styles defined below are those used by WordPress core for Skip Links.
If you’re using the class ‘.screen-reader-text’ on any other focusable element (buttons, links, or form fields), then these focus styles will also apply. If this is the case, you may need to change the positioning rules, depending on the location of the focusable element.