Please help us help you and fill where relevant:
Your LimeSurvey version: LimeSurvey Cloud Version 6.16.1
Own server or LimeSurvey hosting: LimeSurvey Hosting 
Survey theme/template: fruity_TwentyThree (but I tried extending it and the extended version does not show up in Theme drop-down in my survey)
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Hi guys. I just installed LimeSurvey 2 days ago just to learn how it works. So I haven't messed around with the configurations at all. I am proficient with decipher and confirmit.
I want to know how to do CSS and JavaScript in my surveys. The tutorial says to extend an existing theme and edit custom.css from there. I did just that. I just placed a simple css code in custom.css
.Q1code {
  color: blue 
}
<!-- Q1code is the class name I listed for my Q1 question -->
When I saved that and go to the themes in general settings for my survey, the extended theme does not show up. My question is not updated.
I tried clearing cache in global settings, deleted and reextended, uninstall/install the theme, nothing worked.
CSS, I can at least do that in Edit HTML but it doesn't work with JavaScript. Any help would be much appreciated.
 

whew. nevermind. I wasted 2 days on limesurvey just to attempt to get a basic functionality to work. I guess I'm just gonna try other survey sites like OpinionX, SurveyMonkey or Conjointly. I'm definitely not gonna spend money just to use javascript.

You don't have to spend money to use Javascript. You said you installed it, so I assume you are using the community edition (self hosted), not the Limesurvey Cloud hosting (which has a free version with limits in sample size, just for testing, and paid plans). You just need to switch off the XSS filter or create surveys as a super-admin and you can include Javascript code.

In any way, I think you made up your mind already on using an other survey tool, which is totally fine. Limesurvey has it's quirks and doesn't fit everyone.