Responsive todo app with day and night modes

This is probably the most genuinely useful thing I've built so far. I built the functionality pretty quickly, but took a little longer with the styling. To those who have built this one: what was your biggest challenge with the project?

Some things that were new to me:

• The content <template> element
• Adding a gradient border with border radius and the ::before pseudo-class
• Bonus: Implemented localStorage, so users won't lose their todos on page refresh

Some things I did not include in v1:

• Finessed transitions for creating/deleting todos, toggling day/night modes, or any of the hover states
• UPDATE: Added drag and drop on 11/7 (built from scratch using VanillaJS - desktop only)