body {
    background: url('/Users/allisonbrett/Projects/Therapy3/1918.jpeg') no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
}

.test {
  color: red;
}

body {
    background: url('https://github.com/allisonPlusPlus/therapy3/blob/master/1918.jpeg?raw=true') no-repeat center center fixed;
    -webkit-background-size: cover;
    -moz-background-size: cover;
    background-size: cover;
    -o-background-size: cover;
}

Add full path to background image
Add full path to background image
