Default setting: background-size: auto;
Absolute resize of width, retaining aspect ratio: background-size: 100px;
Absolute resize of width and height, losing aspect ratio: background-size: 100px 250px;
Resize relative to container width, retaining aspect ratio: background-size: 50% auto;
Resize relative to container height, retaining aspect ratio: background-size: auto 100%;
Image covers container, is cropped and retains aspect ratio: background-size: cover;
Image stretched to fit container dimensions and retains aspect ratio: background-size: contain;
Sizing multiple backgrounds: background-size: 240px 210px, auto, 150px;