How can I change the main CSS codes?

[ogulcan1787 (Ogulcan)]

Hi, I made many CSS changes by adding CSS codes to the theme settings.
Do these codes slow down the website?
Can I change these codes directly from within the main theme?
Thank you in advance for your help.

[merefield (Robert)]

You are best to start here:

Beginner's guide to developing Discourse Themes

So, you want to create Discourse themes? Not sure where to start? Or maybe you have created Discourse themes before, but want to learn how to do even more cool things. Well, you’ve come to the right place Developer’s guide to Discourse Themes Subjects include a general overview of Discourse themes, creating and sharing Discourse themes, theme development examples, searching for and finding information / examples in the Discourse repository, and best practices. Prerequisites: …

and it will not slow your site down.

[Lilly]

I have posted CSS help to you many times. please read the links that people provide you for information.

Search section like on Reddit?

If you are trying to learn to customize your forum, please take some time to learn some basics of themes, components and CSS. Alternatively, you can always post in marketplace for paid help to customize your forum.