Possible to insert custom HTML or Javascript?

I saw that there is the ability to edit theme code. However, whenever I insert my custom javascript or HTML it doesn't seem to work. For context, the code I want to insert is for a chatbot and a section of the code is as follows:

<widgetbot server="xxx" channel="xxx" shard="https://emerald.widgetbot.io" width="800" height="600" ></widgetbot> <script src="https://cdn.jsdelivr.net/npm/@widgetbot/html-embed"></script>

Any idea how to fix this please?

Thanks.