Why :before cannot be seen in safari?

问题

I have a code which works brilliant in Chrome:

#menu ul {
list-style-position: inside;
list-style-type: none;
display: block;
margin: 0 auto;
padding: 0;
}
#menu li {
font-size: 11px;
width: 95px;
display: inline-block;
vertical-align: top;
position: relative;
}
#menu li a {
color: black;
text-decoration: none;
}
#menu li a img {
opacity: 0;
filter: alpha(opacity=0);
-moz-opacity: 0;
position: absolute;
top: 0;
left: 22px;
margin: 0 auto;
-webkit-transition: opacity 0.2s linear;
-moz-transition: opacity 0.2s linear;
-o-transition: opacity 0.2s linear;
-ms-transition: opacity 0.2s linear;
}
#menu li a:hover img {
opacity: 1.0;
filter: alpha(opacity=100);
-moz-opacity: 1.0;
}
#menu li a:before {
content: "";
display: block;
background: url('../images/greece.gif') no-repeat center;
width: 50px;
height: 50px;
margin: 0 auto;
opacity: 1.0;
filter: alpha(opacity=100);
-moz-opacity: 1.0;
-webkit-transition: opacity 0.2s linear;
-moz-transition: opacity 0.2s linear;
-o-transition: opacity 0.2s linear;
-ms-transition: opacity 0.2s linear;
}
#menu li.news a:before {
background: url('/images/menu/4.gif') no-repeat center;
}
#menu li a:hover:before {
opacity: 0;
filter: alpha(opacity=0);
-moz-opacity: 0
}
#menu li a span.image-title {
display: block;
padding: 5px;
}
#menu li:hover a, #menu li.current.active a {
color: red;
}

I do not want to use such crazy code, but I have no other way 'cause I'm working with joomla 2.5

So what I have as a result... In firefox doesn't work opacity transition. No, itworks, but in a strange way... Tolerably.

In Safari :before are not shown at all!

Web-site with this problem (not an ad).

回答1:

Check this out : http://caniuse.com/#feat=css-gencontent and check on "known issue" tab. Safari browser did not support transitions on pseudo element. I face the same issue yesterday.

回答2:

just add position:absolute

a:before{
position:absolute;
content:"";
top: 0px;
left: 0px;
.....

and make sure you ve position relative on a

#menu li a{
position:relative;
}

for example this works well

#menu li a:before {
content: "";
display: block;
background: url('../images/greece.gif') no-repeat center;
width: 50px;
height: 50px;
position: absolute;
opacity: 1.0;
filter: alpha(opacity=100);
-moz-opacity: 1.0;
-webkit-transition: opacity 0.2s linear;
-moz-transition: opacity 0.2s linear;
-o-transition: opacity 0.2s linear;
-ms-transition: opacity 0.2s linear;
}

very important for for css3 dev box-sizing

*, *:after, *:before  {
outline: none;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
padding:0;
margin:0;
}

:before and :after are always position:absolute and the main element should be position relative

来源：https://stackoverflow.com/questions/17989772/why-before-cannot-be-seen-in-safari