CSS feature detection using feature queries

feature-query.css

/*
@supports(test condition) {
  apply rules
}
@supports not(test condition) {
  apply rules
}
*/
/* use CSS variable */
@supports (background-color: var(--bg-color)) { /* support: http://caniuse.com/#feat=css-variables */
  body {
    background-color: var(--bg-color);
  }
}
@supports not(background-color: var(--bg-color)) {
  body {
    background-color: #ff6347;
  }
}