Hi,
There is not an officially supported way to do these sorts of customizations yet. You will have to make CSS changes in the code or write your own plugin.
Examples of changing Kibana UI:
Here are a couple of posts for changing logo: Replace the kibana logo?
And here are Kibana plugins:
https://www.elastic.co/guide/en/kibana/current/known-plugins.html
Thanks,
Rashmi