Complete to-do list with a custom drag-n-drop, active LocalStarage

Greetings! There is my solution for a lovely and challenging project of to-do list :)

Some feature that I am proud of:

• All task features are made: create/delete items, filter, clear all, drag-n-drop, light/dark themes
• Fully responsive
• Drag-n-drop potential drop area highlight
• Working Local Storage (all items and states remain even after page reload)
• New item auto resize depending on lines amount
• Small enhancement, but though: I added empty state for the starter screen :)

Questions:

1. When I start dragging there is "x" icon appear above random list item. How to avoid this behavior?
2. What topics should I learn to make this project cross browser?