Hi @conwayxu, the 50px of padding on each side of the image is what is cutting off the rounded corners. To keep the rounded corners and the space on each side, remove the padding then set the image width to 80%, then set the right and left margin to auto.
Changes made in the navigator alter the HTML of your website and this effects all breakpoints. Instead, give a class to the element you want to change, then adjust that class for each view. You can use Display: None to hide an element on a particular breakpoint, then set it back to Block when you want it to show up. The same goes for grids - simply give the grid a class, then you can adjust its properties (columns, rows, gap, etc.) for each breakpoint.
Hope that helps!