You can use the property background-size to resize background images:
background-size: 100px 50px /* set size to 100 x 50 pixels */ background-size: 100% 100% /* set size to 100% of the size of the containing element */ background-size: 50% /* set width to 50% of the width of the containing element and keeps the aspect ratio of the image */ background-size: auto 80px /* set height to 80 pixels and keeps the aspect ratio of the image */ background-size: cover /* set size so that image completely covers the area */ background-size: contain /* set size so that image completely fits the area */