Attention Popup Screen Cover Only With CSS

put this code at above </b:skin>

/* style link popup */
a.popup-link {
padding:17px 0;
text-align: center;
margin:10% auto;
position: relative;
width: 300px;
color: #fff;
text-decoration: none;
background-color: #FFBA00;
border-radius: 3px;
box-shadow: 0 5px 0px 0px #eea900;
display: block;
}
a.popup-link:hover {
background-color: #ff9900;
box-shadow: 0 3px 0px 0px #eea900;
-webkit-transition:all 1s;
transition:all 1s;
}
/* end link popup*/

/* animation popup */
@-webkit-keyframes autopopup {
from {opacity: 0;margin-top:-200px;}
to {opacity: 1;}
}
@-moz-keyframes autopopup {
from {opacity: 0;margin-top:-200px;}
to {opacity: 1;}
}
@keyframes autopopup {
from {opacity: 0;margin-top:-200px;}
to {opacity: 1;}
}
/* end animation popup */

#popup {
background-color: rgba(0,0,0,0.8);
position: fixed;
top:0;
left:0;
right:0;
bottom:0;
margin:0;
-webkit-animation:autopopup 2s;
-moz-animation:autopopup 2s;
animation:autopopup 2s;
}
#popup:target {
-webkit-transition:all 1s;
-moz-transition:all 1s;
transition:all 1s;
opacity: 0;
visibility: hidden;
}

@media (min-width: 768px){
.popup-container {
width:600px;
}
}
@media (max-width: 767px){
.popup-container {
width:100%;
}
}
.popup-container {
position: relative;
margin:7% auto;
padding:30px 50px;
background-color: #fafafa;
color:#333;
border-radius: 3px;
}
a.popup-close {
position: absolute;
top:3px;
right:3px;
background-color: #333;
padding:7px 10px;
font-size: 20px;
text-decoration: none;
line-height: 1;
color:#fff;
}
.popup-form {
margin:10px auto;
}
.popup-form h2 {
margin-bottom: 5px;
font-size: 37px;
text-transform: uppercase;
}
.popup-form .input-group {
margin:10px auto;
}
.popup-form .input-group input {
padding:17px;
text-align: center;
margin-bottom: 10px;
border-radius:3px;
font-size: 16px;
display: block;
width: 100%;
}
.popup-form .input-group input:focus {
outline-color:#FB8833;
}
.popup-form .input-group input[type="email"] {
border:0px;
position: relative;
}
.popup-form .input-group input[type="submit"] {
background-color: #FB8833;
color: #fff;
border: 0;
cursor: pointer;
}
.popup-form .input-group input[type="submit"]:focus {
box-shadow: inset 0 3px 7px 3px #ea7722;}



Put anywhere in the body
this code :

<div class=”popup-wrapper” id=”popup”>
<div class=”popup-container”>
<!– START CONTENT –>
<h2>ATTENTION... !!</h2>
..... your content attention here ...
<!– END CONTENT –>
<a class=”popup-close” href=”#popup”>X</a>
</div>
</div>


This popup that appear only on the home page only
add the code below :

<b:if cond="data:blog.url == data:blog.homepageUrl">
<div class=”popup-wrapper” id=”popup”>

......................... 

</div>
</b:if>


 DEMO  : 

click here