CSS字符串规范

字符串、URL 应该始终被单引号(‘)所包裹，initial 或 sans-serif 的专用名词无须引用起来

// Yep
$direction: 'left';

// Nope
$direction: left;

// Yep
.foo {
  background-image: url('/images/kittens.jpg');
}

// Nope
.foo {
  background-image: url(/images/kittens.jpg);
}

// Yep
$font-type: sans-serif;

// Nope
$font-type: 'sans-serif';

// Okay I guess
$font-type: unquote('sans-serif');

// Okay
@warn 'You can\'t do that.';

// Okay
@warn "You can't do that.";