Further Info on Popup windows

CSS rules can be changed in both the Developer Tools Elements/Styles tab and by injecting code in the console. In the console, any rule can be changed and displayed, but the Elements/Styles tab gives further insight. CSS rules affect all of the presentation of the webpage, so changing styles can be very powerful.

See the below links for learning about editing CSS:

Editing styles in Chrome Editing styles in Firefox Editing styles in Safari Editing styles in IE

You can edit style in the console likewise:

document.getElementById("id").style.rule = value//sets CSS rule
document.getElementById("id").style.rule = color//sets colour rule
document.getElementById("id").style.rule = backgroundColor//sets background-color rule

Note: If the name of the CSS rule has a hyphen in it, like font-size, it will be changed to one word with camelCase, like fontSize