Make search box bigger and centre it

Hey there! I am trying to style my members page and have come across some trouble trying to make search box bigger and centre it on all devices. Please help me with css solution. I have a problem changing layout without making the site look terrible on smaller screens. If you could share a good read that can help me change the layout of pages without messing up appearance on smaller screens I would really appreciate it. I am also waiting a while now for response on this topic, so please look at that too if you can..
Thanks and hope you have a nice day,
Mwale