where to put custom css

An easy way to add custom CSS is to install the Jetpack plugin and activate the Custom CSS module. You’ll then add your custom CSS in the new stylesheet editor that’ll appear in your dashboard, under Appearance > Edit CSS. You could also install a standalone custom CSS plugin if you prefer.

Whatever you do, don’t edit the theme files directly, otherwise your changes will be overwritten every time the theme is updated.

Let me know how it goes!

Each plugin has its own support forum where you can get help.

Simple Custom CSS has good ratings, you might want to give it a try:

https://ww.wp.xz.cn/plugins/simple-custom-css/

Installation guide: https://ww.wp.xz.cn/plugins/simple-custom-css/installation/

If you run into any trouble you can post in their forum: https://ww.wp.xz.cn/support/plugin/simple-custom-css

On WordPress.com, there is a custom CSS editor built right into the Customizer. Custom CSS is a feature available with the Premium or Business plans.

These forums are for folks running the WordPress software on their own hosting, not on WordPress.com. If you need further help with your theme on WordPress.com, feel free to post in the themes forum here:
https://en.forums.wordpress.com/forum/themes

If you need further CSS help specifically, post in our CSS Customization forum.

Here are some tips on getting help in the WordPress.com forums: http://en.support.wordpress.com/getting-help-in-the-forums/

You can also access the live chat support option when available here:

https://wordpress.com/help/contact

That’s right, Custom CSS is only available with the Premium or Business plan on WordPress.com. But do feel free to post in the themes forums and explain your goal, providing a link to your site. We might be able to find a workaround for you’re trying to do that doesn’t require CSS. See you there!