Site Header Editing

Hi, Apologies if this is a poor description of my question as I am new to this. On my draft website https://bluelizard.com.au   I have the site header hidden using the plugin "Hide Title". I have created a draft Banner to replace the title as I wanted the background image to be visible. As a result there is a large gap between the top of the page and the header image. My question is is there a plugin or a way to design a better looking heading with transparency or the ability to add a shadow to the text? Alternatively can I add CSS that will reduce the size of the site header block reducing the size of the gap? Also if you can suggest another way. I have played around with Site Identity and searched the web without success but this is probably due to my lack of experience on the topic. I would be grateful for any help Simon Davies