Inject Custom Code into a Text Box

Hi Guys,

So I have a request which should be fairly simple but I'm having trouble implementing this functionality and could use some help. I have a text box that I want to add some code to. Essentially I want to use JavaScript to inject an image for a logo where the current text is but I'm having trouble figuring out how to add a code block in that particular area. Please see the attached picture. I want to inject an image where it says 'This is a test'. Is this possble?

Can you share link to page in screenshot?

You can also use Markdonw Block or Code Block to achieve this.