When using Inspect in Chrome, want to save CSS locally so I can experiment

I’m a designer and I’m working with a web developer on a site. I don’t have a dev environment and don’t plan to get one. I want to experiment with the site’s CSS to improve the design, but any changes I make get wiped out when I switch to a new page on the site. Is there a way to save my CSS and HTML changes locally without having to save them back to a server?

Access to Chrome extension elements from frontend

Can I interact with elements of the specific Chrome Extension (e.g. click on a button of the extension) in JS script of my frontend?

What does the waterfall diagram in the given screenshot taken with chrome dev tool means?

Below given is the screenshot was taken while running my application with the dev tool in chrome. Please help me to understand the waterfall diagram. What the green and blue color refers to. My application renders content after a long delay, so I used dev tool to understand my application behaviour. Can I be able to understand the delay that my application make with this diagram?

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