.slide {
		position: relative;
		margin: 10px 10px 30px 10px;
		display: block;
		min-height: 550px;
		padding: 20px;
		box-sizing: border-box;
		font: 17px SVN-Georgia;
		color: #ffffff;
		text-align: justify;
		text-shadow: #000 1px 1px 1px;
		background-image: 
			radial-gradient( circle at left 30%, 
			rgba(34, 34, 34, 0.2), 
			rgba(34, 34, 34, 0.2) 80px, 
			rgba(34, 34, 34, 0.3) 100px, 
			rgba(51, 51, 51, 0.3) 160px, 
			rgba(51, 51, 51, 0.3)), 
			linear-gradient( 215deg, transparent, transparent 100px, 
			rgba(34,34,34,0.4) 260px, rgba(34,34,34,0.4) 320px, transparent), 
			radial-gradient( circle at right, rgba(17,17,17,0.4), rgba(51, 51, 51, 0.5)),
			linear-gradient(0deg, rgba(80,80,80,.5) , rgba(80,80,80,.2) 70% );
		background-color: rgba(51, 51, 51, 0.8);
		border: tan solid 12px;
		border-top: #bda27e solid 12px;
		border-left: #b19876 solid 12px;
		border-bottom: #c9ad86 solid 12px;
		box-shadow: 0px 0px 6px 5px rgba(58, 18, 13, 0), 
			0px 0px 0px 2px #c2a782, 0px 0px 0px 4px #a58e6f, 
			3px 4px 8px 5px rgba(0, 0, 0, 0.5);
	}
	.slide_menu {
		position: absolute;
		right: 5px;
		bottom: -2px;
	}
	.slide_menu span {
		display: inline-block;
		padding: 2px 10px;
		margin: 2px;
		color: #000;
		font-size: 12px;
		text-shadow: none;
		border-radius: 2px;
		box-shadow: 1px 1px #888;
	}
	.slide_menu span:nth-child(1) {
		background-color: #fff;
	}
	.slide_menu span:nth-child(2) {
		background-color: yellow;
	}
	.slide_menu span:nth-child(3) {
		background-color: cyan;
	}
	.slide_intro {
		margin: 150px 20px;
	}
	.slide_intro .slide_intro_name {
		text-align: center;
		color: crimson;
		font: bold 40px DDC;
		line-height: 47px;
		text-transform: uppercase;
		padding: 20px;
		background: chartreuse;
		-moz-border-radius: 5px;
				-webkit-border-radius: 5px;
				border-radius: 5px;
	}
	.slide_intro .slide_intro_teacher {
		text-align: center;
		font: bold 25px DDC;
		padding: 20px;
	}
	.slide_intro .slide_intro_teacher b {
		color: yellow;
		text-transform: uppercase;
	}
	.slide h2 {
		font: 24px DDC;
		color: yellow;
		font-weight: bold;
	}
	.slide h3 {
		font: 20px LaTeX;
		color: magenta;
		font-weight: bold;
	}
	.slide h4 {
		font-size: 19px;
		color: cyan;
		font-weight: bold;
	}
	.slide .list2cot {
		-moz-column-count: 2;
		-moz-column-gap: 20px;
		-webkit-column-count: 2;
		-webkit-column-gap: 20px;
		column-count: 2;
		column-gap: 20px;
	}
	.slide .list3cot {
		-moz-column-count: 3;
		-moz-column-gap: 20px;
		-webkit-column-count: 3;
		-webkit-column-gap: 20px;
		column-count: 3;
		column-gap: 20px;
	}
	.slide .list4cot {
		-moz-column-count: 4;
		-moz-column-gap: 20px;
		-webkit-column-count: 4;
		-webkit-column-gap: 20px;
		column-count: 4;
		column-gap: 20px;
	}
	.slide .khung {
		padding: 10px;
		display: inline-block;
		border: 3px solid #00ffff;
		border-radius: 2% 6% 5% 4% / 1% 1% 2% 4%;
		min-width: 50%;
		margin: 10px 0;
		position: relative;
		
		&::before {
			content: '';
			border: 2px solid #ffffff;
			display: block;
			width: 100%;
			height: 100%;
			position: absolute;
			top: 50%;
			left: 50%;
			transform: translate3d(-50%, -50%, 0) scale(1.015) rotate(0.5deg);
			border-radius: 1% 1% 2% 4% / 2% 6% 5% 4%;
		}
	}
	.slide .vidu {
		margin: 10px 0;
	}
	.slide .vidu .vidu_cau {
		font: 17px LaTeX;
		font-weight: bold;
		color: #00ffff;
	}
	.slide table {
		margin-left: auto;
  		margin-right: auto;
		color: #fff;
		border: 1px solid #fff;
		-webkit-box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.9), 0 1px 2px rgba(0, 0, 0, 0.1);
		box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.9), 0 1px 2px rgba(0, 0, 0, 0.1);
		-moz-border-radius: 2px;
				-webkit-border-radius: 2px;
				border-radius: 2px;
	}
	.slide table td {
		padding: 5px;
	}
	.slide img {
		max-width: 100%;
		-moz-border-radius: 3px;
				-webkit-border-radius: 3px;
				border-radius: 3px;
	}
	.slide ul {
        list-style-position: outside;
        list-style-type: '👍';
        margin-bottom: -5px;
    }

	.ex {
		background: white;
		padding: 10px;
		text-shadow: none;
		color: #000;
		-webkit-box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.9), 0 1px 2px rgba(0, 0, 0, 0.1);
		box-shadow: inset 0 0 0 1px rgba(255, 255, 255, 0.9), 0 1px 2px rgba(0, 0, 0, 0.1);
		-moz-border-radius: 2px;
				-webkit-border-radius: 2px;
				border-radius: 2px;
	}
	.ex .ex_pin {
		text-align: center;
		margin: -15px 0 -10px 0;
		border: none;
		box-shadow: none;
		border-radius: 0px;
	}
	.ex .ex_choice .ex_choice_item {
		text-align: left;
		margin: 0px 0px 5px 5px;
		border: 1px solid #ccc;
			-moz-border-radius: 3px;
				-webkit-border-radius: 3px;
				border-radius: 3px;
	}
	.ex .ex_choice .ex_choice_item div {
		width: auto;
		font-weight: bold;
		color: blue;
		display: inline-block;
		padding: 0 5px 0 4px;
		margin: -3px 3px 0px 0px;
		border: 1px solid #ccc;
			-moz-border-radius: 25px;
			-webkit-border-radius: 25px;
			border-radius: 25px;
	}
	.ex .ex_choice .ex_choice_item a {
		display: block;
		text-decoration: none;
		color: #000;
		padding: 7px 5px 5px 5px;
	}
	.ex .ex_choice .ex_choice_item:hover {
		border: 1px solid gray;
	}
	.ex .ex_choice input[type=radio]{
		position: absolute;
		visibility: hidden;
	}

	@media screen and (min-width: 800px) {
		.ex {
			width: 700px;
			margin: 10px auto;
		}
	}

	@media screen and (max-width: 799px) {
	}