If you have a Wikipedia account, open your Preferences, go to the Appearance tab, and edit the Custom CSS for the Vector skin. Paste the contents of style.css into the editor, and save. For better alignment of mathematical equations, enable MathML or Mathjax in the Appearance tab. Alternatively, you can load the CSS using a browser plugin (such as Stylish for Firefox or Stylish for Chrome) for the domain https?://*.wikipedia.org.