/* 枠の太さ = 40px */
/* 枠の色 = #fff */

	html:before,
	html:after,
	body:before,
	body:after {
	  content: "";
	  background: #fff;
	  position: fixed;
	  display: block;
	  z-index: 1;
	}

	/* 上 */
	html:before {
	  height: 40px; 
	  width: 100vw;
	  left: 0;
	  top: 0;
	}

	/* 右 */
	html:after {
	  width: 40px;
	  height: 100vh;
	  right: 0;
	  top: 0;
	}

	/* 下 */
	body:before {
	  height: 40px;
	  width: 100vw;
	  bottom: 0;
	  left: 0;
	}

	/* 左 */
	body:after {
	  width: 40px;
	  height: 100vh;
	  top: 0;
	  left: 0;
	}

@media screen and (max-width:640px){
	/* 上 */
	html:before {
	  height: 20px; 
	}

	/* 右 */
	html:after {
	  width: 20px;
	}

	/* 下 */
	body:before {
	  height: 20px;
	}

	/* 左 */
	body:after {
	  width: 20px;
	}
}