The Custom code settings page
You should only add custom code if you know what you're doing.
The Custom CSS section is where you can add CSS to change the look of your tabs.
The CSS is added internally though a
<style> tag in the document
<head>, so it won't slow down the loading of your shop or tabs in any way.
<script> tag that's rendered right before the closing
</body> tag, so it won't slow down the loading of your shop or tabs in any way.