Tom Watts

Hi apologies if this has been asked before. I have trawlled through many pages of support but I haven't managed to find what I am after. I would like for my banner ads to be set to display at the full width of the space available. In particular I would like to drop the invocation code for my leaderboard (728x90) into my wordpress editorial content which is 620 wide on a desktop. I would like this ad to show the whole banner regardless of whether on a phone or desktop etc. I'm hoping there is a simple snippet of code I need to add to make this happen? I really hope you can help? Cheers Tom