The sizes attribute paired with the srcset attribute provides information on how much space these images take up within the viewport at different browser breakpoints, but the aspect ratios should remain the same across those breakpoints. Once the sizes option is selected, you can let the browser know the size of this image in relation to the site layout, using the <em>Sizes</em> field. For a hero image that always fills the entire screen, you could simply enter 100vw, which means 100% of the viewport width. For an image that fills 90% of the screen for small viewports, but only fills 40% of the screen when the viewport is larger than 40em (typically 640px), you could enter "(min-width: 40em) 40vw, 90vw" in the Sizes field. The last item in the comma-separated list is the smallest viewport size: other items in the comma-separated list should have a media condition paired with an image width. <em>Media conditions</em> are similar to a media query, often a min-width paired with a viewport width using em or px units: e.g. (min-width: 640px) or (min-width: 40em). This is paired with the <em>image width</em> at that viewport size using px, em or vw units. The vw unit is viewport width and is used instead of a percentage because the percentage always refers to the width of the entire viewport.