Difference between "Seite öffnen" and "Öffne die Seite"

1. Seite öffnen - Open the page
2. Öffne die Seite - Open the page (present tense imperative?)

The same applies to:

1. Fenster schließen - close the window
2. Schließe das Fenster - close the window (present tense imperative?)

What am I missing?If I understand correctly they both have the same meaning, but I couldn't find a grammar rule for the first sentence in each section. What is it called? Why we use infinitive there?

Can you please explain the difference between these two examples?