Center responsive absolutely positioned element with fixed margins - html

Question

I have an absolutely positioned CSS banner that has a responsive width and height based on viewport size. The element is centered on desktop and tablet devices, but not on mobile (when the banner's width starts to shrink).
I can't use the classic margin: 0 auto; trick because the margins have to be set to a fixed value for the banner to work.
The code is below:
HTML:
<h1 class="banner">A Simple CSS Banner</h1>
CSS:
#import url(https://fonts.googleapis.com/css?family=Rye);
body
{ background: #eee; }
.banner {
position: absolute;
left: 50%;
display: block;
margin: 100px -200px;
width: 400px;
max-width: calc(100% - 150px);
height: 60px;
border: 1px solid #8a1;
font: normal 30px/60px 'Rye';
text-align: center;
color: #451;
background: #9b2;
border-radius: 4px;
box-shadow: 0 0 30px rgba(0,0,0,.15) inset,
0 6px 10px rgba(0,0,0,.15);
}
.banner::before,
.banner::after {
content: '';
position: absolute;
z-index: -1;
left: -70px;
top: 24px;
display: block;
width: 40px;
height: 0px;
border: 30px solid #9b2;
border-right: 20px solid #791;
border-bottom-color: #94b81e;
border-left-color: transparent;
transform: rotate(-5deg);
}
.banner::after {
left: auto;
right: -70px;
border-left: 20px solid #791;
border-right: 30px solid transparent;
transform: rotate(5deg);
}
#media (max-width: 475px) {
.banner {
height: 90px;
line-height: 45px;
}
.banner::before,
.banner::after {
border-width: 45px;
border-right-width: 30px;
}
.banner::after {
border-left-width: 30px;
border-right-width: 45px;
}
}
Link to working codepen: https://codepen.io/Adam0410/pen/QZOKdV
Thanks for the help!

Answer 1

Check if this helps you.
#import url(https://fonts.googleapis.com/css?family=Rye);
body {
background: #eee;
}
.banner {
position: absolute;
left: 50%;
transform: translate(-50%);
display: block;
margin: 100px 0;
width: 400px;
max-width: calc(100% - 150px);
min-height: 60px;
}
.banner span {
display: block;
position: relative;
z-index: 1;
border: 1px solid #8a1;
font: normal 30px/60px "Rye";
text-align: center;
color: #451;
background: #9b2;
border-radius: 4px;
box-shadow: 0 0 30px rgba(0, 0, 0, 0.15) inset, 0 6px 10px rgba(0, 0, 0, 0.15);
}
.banner::before,
.banner::after {
content: "";
position: absolute;
z-index: -1;
left: -70px;
bottom: -24px;
display: block;
width: 40px;
height: 0px;
border: 30px solid #9b2;
border-right: 20px solid #791;
border-bottom-color: #94b81e;
border-left-color: transparent;
transform: rotate(-5deg);
}
.banner::after {
left: auto;
right: -70px;
border-left: 20px solid #791;
border-right: 30px solid transparent;
transform: rotate(5deg);
}
#media (max-width: 475px) {
.banner {
min-height: 90px;
line-height: 45px;
}
.banner::before,
.banner::after {
border-width: 45px;
border-right-width: 30px;
}
.banner::after {
border-left-width: 30px;
border-right-width: 45px;
}
}
<h1 class="banner"><span>A Simple CSS Banner</span></h1>

Answer 2

You can simply use Media queries and adapt Width and margin.
something like:
media (max-width: 475px) {
.banner{
width: 200px;
margin:100px -100px;
}
}

Answer 3

This way you keep the top and bottom margin:
left: 0; right: 0;
margin: 100px auto;

Answer 4

If you want to center an absolute or fixed element you should :
position: absolute;
left: 0%;
right:0%;
margin: 0 auto;