FuzzGuard

Want to style your Admin login pages for your clients in their corporate colors? Sick of the default wordpress wp-admin login page? Then this plugin maybe for you. It allows you to style the WordPress Admin Panel login page that comes default with every wordpress installation.
You can do the following:
<pre><code>* Upload and set your own logo for the Admin Panel login page
* Upload and set your own logo for the Admin Panel Menu (This replaces the DASHBOARD menu option)
* Set the background color of the Admin Panel login page
 * Set the background colour of the Username/Password boxes.
 * Set the background colour of the 'Log in' button
 * Set the background color of the Login Box.
* Set the color of the footer text.
* Set the colour of the text in the Login box.
* Set the colour of the 'Log in' text on the 'Log in' button 
* Set to have CSS rounded corners on your login box and the 'Log in' button
</code></pre>
Usually this require’s modification of CSS code to have the changes stick. This can lead to changes being overwritten on theme updates. This plugin is simple and allows you to easily change the options between your custom choices and the default ones that are set for your theme.

Style Admin

Want to style your Admin login pages for your clients in their corporate colors?  Sick of the default wordpress wp-admin login page?  Then this plugin …

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.

Style Admin vs TJ Custom CSS