<h1>Popup/Modal Windows without JavaScript</h1>
<div class="box">
	<a class="button" href="#">Login /signup</a>
</div>

<div id="popup1" class="overlay">
	<div class="popup">
		<h2>Here i am</h2>
		<a class="close" href="#popup1">&times;</a>
		<div class="content">
			Thank to pop me out of that button, but now i'm done so you can close this window.
		</div>
	</div>
</div>

*, *:after, *:before {
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  box-sizing: border-box;
}
body {
  font-family: Arial, sans-serif;
  background: url(http://www.shukatsu-note.com/wp-content/uploads/2014/12/computer-564136_1280.jpg) no-repeat;
  background-size: cover;
  height: 100vh;
}

h1 {
  text-align: center;
  font-family: Tahoma, Arial, sans-serif;
  color: #06D85F;
  margin: 100px 0;
}

.box {
  width: 40%;
  margin: 0 auto;
  background: rgba(255,255,255,0.2);
  padding: 35px;
  border: 2px solid #fff;
  border-radius: 20px/50px;
  background-clip: padding-box;
  text-align: center;
}

.button {
  font-size: 1em;
  padding: 10px;
  color: #fff;
  border: 2px solid #06D85F;
  border-radius: 20px/50px;
  text-decoration: none;
  cursor: pointer;
  transition: all 0.3s ease-out;
}
.button:hover {
  background: #06D85F;
}

.popup h2 {
  margin-top: 0;
  color: #333;
  font-family: Tahoma, Arial, sans-serif;
}
.popup .close {
  position: absolute;
  top: 20px;
  right: 30px;
  transition: all 0.2s;
  font-size: 30px;
  font-weight: bold;
  text-decoration: none;
  color: #333;
}
.popup .close:hover {
  color: #06D85F;
}
.popup .content {
  max-height: 30%;
  overflow: auto;
}

/*Let's make it appear when the page loads*/
.overlay:target:before {
    display: none;
}
.overlay:before {
  content:"";
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  display: block;
  background: rgba(0, 0, 0, 0.6);
  position: fixed;
  z-index: 9;
}
.overlay .popup {
  background: #fff;
  border-radius: 5px;
  width: 30%;
  position: fixed;
  top: 0;
  left: 35%;
  padding: 25px;
  margin: 70px auto;
  z-index: 10;
  -webkit-transition: all 0.6s ease-in-out;
  -moz-transition: all 0.6s ease-in-out;
  transition: all 0.6s ease-in-out;
}
.overlay:target .popup {
    top: -100%;
    left: -100%;
}

@media screen and (max-width: 768px){
  .box{
    width: 70%;
  }
  .overlay .popup{
    width: 70%;
    left: 15%;
  }
}