Marius L. J.

Personalise your own website, no matter what theme and what customization options are added by the themes creator.
When active, the plugin will add a new section to your Customize screen entitled Simple Customize, containing input fields for various elements needed to display a new customize option.
You can easily find what you wish to customize by using the Find element button, which will let you point and click in the preview window to find what you are looking for. 
Although no prior knowledge of CSS or HTML is required to use the plugin, basic understanding of CSS will definitely help you make the most out of this plugin, an in turn your own site.
Once you are happy with everything in the options, use the Add element button to have your customize option implemented. 
The CSS will be queued up in such a manner that it will try to be the dominant rule, so assuming the theme doesn’t have any <a href="http://stackoverflow.com/questions/3706819/what-are-the-implications-of-using-important-in-css" rel="nofollow ugc">!important</a> flags on its styling, your own styling will appear.
You are also able to implement 3rd party fonts using the plugins own options page, where you may add manual styling alternatives, as well as create categories for grouping your own styles.
All customizations are theme-specific, this means if you ever change your theme, you will get a clean slate to work off when customizing it. 
Of course, should you ever revert back to your old theme, your previous custom styling will still be there.
Note: You should always be cautious of modifying other peoples work, respect the time and dedication put forth by your themes author.

Simple customize

binarymoon

Bartosz Gadomski

Teydea Studio

A simple way to customise the login screen on your WordPress install. There are a number of advantages to using this plugin:
<ol>
<li>Using a plugin means the changes stay when you upgrade</li>
<li>It’s an easy way to add a little polish to your freelance web design jobs</li>
</ol>

Custom Login

Not too much, not to little, just right.  Allows for custom logo, font and button, and a little extra CSS if needed.  Based on the size of your logo you will need to adjust the background position and/or margins of the #login but with a few tweaks it looks great.  

goldilocks

Customise the WordPress login box quickly and easily

Simple customize vs Custom Login