CSS #1

CSS position:
Absolute positioning

HTML:

<div class="container">
<div class="innter-container">
</div>
</div>

CSS:

.container { position: relative; }
.inner-container { position: absolute }

CSS after and clearfix:
// This will add 'Sample text' after each p element
//  It also can be p:after, but :: is a CSS 3 syntax

p::after {
content: 'Sample text';
}

// Fixing parent container height, when using inner elements with float:right/left

.container::after {
content: '.';
display: block;
height: 0;
clear: both;
}

CSS Triangle:

width: 0;
height: 0;
border-top: 10px solid #000;
border-left: 10px solid transparent;
border-right: 10px solid transparent;

CSS background:

background-image: url(path_to_img), url(path_to_2_img);
background-repeat: no-repeat, repeat;