Images into text element resizing and not being responsive

Hi guys,
when using the text element, if you hit enter you have the option to add an image or embed a video. If I add an image, it looks fine on desktop, but if I use a mobile phone, the image is not responsive. It goes way over the div. If I double click on the image when on the responsive mode (mobile) on UpFront Editor, the image arranges itself well for mobiles. But then, when I switch back on the desktop, the image is really small.
Same, I double click on the small image on the desktop, it arranges itself, but then, if I check the mobile view, the initial issue is back - the image is way over the div.

Any idea what's wrong?

I hope the attached video will explain it better than I did.

Thank you for all your support!