I built my school’s site on Grav and it seems great. My only problem is that when I view the pages from mobile at vertical view the images fit to the screen width but they don’t keep the aspect ratio.
It also happens at my PC when I lessen the width of my browser window.
Thank you. So, my problem was using the TinyMCE editor which doesn’t support markdown commands. With a simple markdown image implementation the images became responsive.