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Font sizes: use ems
Input values and units | Webflow University -
Use HTML5 tags (main, footer and so on)
https://webflow.com/blog/html5-semantic-elements-and-webflow-the-essential-guide -
Also you can add ARIA and other attributes like this:
Custom attributes | Webflow University
About the keyboard - when i test this webflow homepage with keyboard (usingtabs) its also Skipping the dropdowns (so maybe this is a BUG with core Dropdown)
See related wishlist with this specific problem:
https://wishlist.webflow.com/ideas/WEBFLOW-I-862
Reference
For more control try to integrate some Third-party libary like this (change color and so on by widget)
Easy to integrate widget (never try this but its look nice):