Generated by SassMeister.com.

SassMeister-input.scss

// ----
// Sass (v3.3.0)
// Compass (v1.0.0.alpha.18)
// ----

/* 1: nest */
.block {
	background-color: lime;
	.block__elem {
		background-color: olive;
		&.is-hoge {
		  background-color: tomato;
		}
		&:hover {
		  background-color: tomato;
		}
	}
}

/* 2: nest with & */
.block {
	background-color: lime;
	&__elem {
		background-color: olive;
		&.is-hoge {
		  background-color: tomato;
		}
		&:hover {
		  background-color: tomato;
		}
	}
}

/* 3: nest with & (2) */
.block {
	background-color: lime;
	&__elem {
		background: olive;
		&--modifier {
			background: tomato;
		}
	}
}

/* 4: placeholder */
%_block {
	background-color: lime;
	%_block__elem {
		background-color: olive;
		%_block__elem--modifier {
			background-color: orange;
		}
	}
}
.block {
	@extend %_block;
	&__elem {
		@extend %_block__elem;
		&--modifier {
			@extend %_block__elem--modifier;
		}
	}
}

/* 5: placeholder with & */
%_block2 {
	background-color: lime;
	&__elem {
		background-color: olive;
		&--modifier {
			background-color: orange;
		}
	}
}
.block {
	@extend %_block2;
	&__elem {
		@extend %_block2__elem;
		&--modifier {
			@extend %_block2__elem--modifier;
		}
	}
}

/* 6: media rule */
.block {
	background-color: lime;
	&__elem {
		background-color: olive;
	}
	@at-root {
		&__elem2 {
			background-color: olive;
		}
	}
}

/* 7: media rule */
@media print {
	.block {
		background-color: lime;
		@at-root(without:media) {
			background-color: orange;
			&__elem {
				background-color: olive;
			}
		}
	}
}

SassMeister-output.css

/* 1: nest */
.block {
  background-color: lime;
}
.block .block__elem {
  background-color: olive;
}
.block .block__elem.is-hoge {
  background-color: tomato;
}
.block .block__elem:hover {
  background-color: tomato;
}

/* 2: nest with & */
.block {
  background-color: lime;
}
.block__elem {
  background-color: olive;
}
.block__elem.is-hoge {
  background-color: tomato;
}
.block__elem:hover {
  background-color: tomato;
}

/* 3: nest with & (2) */
.block {
  background-color: lime;
}
.block__elem {
  background: olive;
}
.block__elem--modifier {
  background: tomato;
}

/* 4: placeholder */
.block {
  background-color: lime;
}
.block .block__elem {
  background-color: olive;
}
.block .block__elem .block__elem--modifier {
  background-color: orange;
}

/* 5: placeholder with & */
.block {
  background-color: lime;
}
.block__elem {
  background-color: olive;
}
.block__elem--modifier {
  background-color: orange;
}

/* 6: media rule */
.block {
  background-color: lime;
}
.block__elem {
  background-color: olive;
}
.block__elem2 {
  background-color: olive;
}

/* 7: media rule */
@media print {
  .block {
    background-color: lime;
  }
}
.block {
  background-color: orange;
}
.block__elem {
  background-color: olive;
}