You are changing the background image property when a user hovers over the logo. Browsers will not load the background image for any element which is not visibl

You are changing the background image property when a user hovers over the logo. Browsers will not load the background image for any element which is not visible, or where a CSS rule is not active. As a result, the hover version of the logo is only downloaded the first time the user hovers over the logo. A good workaround for this is to create a file with the regular and hover versions of the logo in it, and use the background-position property on hover to show the hover version.