It shows up one image every 5 seconds (one per post). You can go forward and backward using cursor arrows (click inside first to be in context). You could extend this example adding up and down cursor arrows to switch between different tumblrs.
Firefox Nightly version (at least) is going to support (but poorly) HTML input date and HTML input time. You will be able to use natively widgets in updated browsers without depending on third party libraries. However, there are some limitations, if you have ever dealt with an HTML input time you know what it is […]
Forget about any complicated way, just use Flexbox and set up horizontal center and vertical center in the container.
Using fetch with asyncronous functions. This way is even cleaner than using fetch by its own, check this out!