dubhunter

WordPress’s themes are absolutly amazing, except you are not able to theme the login pages very well. 
DBD Login Style is a light weight plugin that will allow you full theme control over the login pages. 
It also offers additional DIV tag creation for custom messages.
Some Features:
<ul>
<li>Specify CSS style sheet for login pages.</li>
<li>Change the URL and TITLE of the header link.</li>
<li>Add specific messages to the different login pages (Login, Registration, Forgot Password)</li>
<li>Change various error messages on login and registration pages.</li>
</ul>

DBD Login Style

Add style to your login page!! This plugin enables you to specify a style sheet to be used on the login page.

Theme Junkie

This plugin will enable a <a href="https://www.theme-junkie.com/plugins/theme-junkie-custom-css/" rel="nofollow ugc">custom css manager</a> on administration page to add Custom CSS code to your WordPress website. It will automatically override any theme or plugin default styles. It also very useful if you want to add customization to your website but do not want to edit your theme or plugin css files.
It comes with two ways to add the custom css code:
1. Setting 
You can go to Appearance → Custom CSS, then you will see a big box/textarea. Put your css code there.
2. Customizer – Live Preview 
If you want to see the live preview while you adding the custom css code, then you can go to Appearance → Customize, after that open the Custom CSS section tab.
<h4>Features Include:</h4>
<ul>
<li>No configuration needed</li>
<li>Live preview</li>
<li>Easy-to-use</li>
<li>Child theme alternative to add customization</li>
<li>Uninstall procedure</li>
</ul>
<h4>Plugin Info</h4>
<ul>
<li>Developed by <a href="https://www.theme-junkie.com/?utm_source=wporg&utm_medium=text_link&utm_campaign=Site%20Promotion" rel="nofollow ugc">Theme Junkie</a></li>
<li>Check out the <a href="https://github.com/themejunkie/theme-junkie-custom-css" rel="nofollow ugc">Github</a> repo to contribute.</li>
</ul>

TJ Custom CSS

Simply works

Easily to add any Custom CSS code to your WordPress website.

DBD Login Style vs TJ Custom CSS