Background

Shorthand

background: #ff0  url(bg.jpg) left top      / 100px auto no-repeat fixed;
background: #abc  url(bg.png) center center / cover      repeat-x  local;
/*          ^     ^           ^             ^            ^         ^
            color image       position      size         repeat    attachment */

Multiple backgrounds

background:
  linear-gradient(to bottom, rgba(0,0,0,0.5), rgba(0,0,0,0.5)),
  url('background.jpg') center center / cover,
  #333;

Other properties

background-clip: border-box | padding-box | content-box [, ...]*; /* IE9+ */
background-repeat: no-repeat | repeat-x | repeat-y;
background-attachment: scroll | fixed | local;
background: url(x), url(y); /* multiple (IE9+) */