夜晚云层动画特效

基于css3 keyframes 属性制作乌云密布云层动画，夜晚云层飘过动画特效。可用于网页动态云层背景特效。这是利用animation 和png云图片制作完成的。

<style>
@keyframes clouds-loop-1 {
  to {
    background-position: -1000px 0;
  }
}
.clouds-1 {
  background-image: url("//img.mukewang.com/60d1d41e00018f2110000447.jpg");
  animation: clouds-loop-1 20s infinite linear;
}

@keyframes clouds-loop-2 {
  to {
    background-position: -1000px 0;
  }
}
.clouds-2 {
  background-image: url("//img.mukewang.com/60d1d3f70001a8ec10000509.jpg");
  animation: clouds-loop-2 15s infinite linear;
}

@keyframes clouds-loop-3 {
  to {
    background-position: -1579px 0;
  }
}
.clouds-3 {
  background-image: url("//img.mukewang.com/60d1d4430001513315790341.jpg");
  animation: clouds-loop-3 17s infinite linear;
}

html, body {
  font-family: sans-serif;
  height: 100%;
  padding: 0;
  margin: 0;
}

body {
  background: url('data:image/svg+xml;base64,PD94bWwgdmVyc2lvbj0iMS4wIiBlbmNvZGluZz0idXRmLTgiPz4gPHN2ZyB2ZXJzaW9uPSIxLjEiIHhtbG5zPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwL3N2ZyI+PGRlZnM+PGxpbmVhckdyYWRpZW50IGlkPSJncmFkIiBncmFkaWVudFVuaXRzPSJvYmplY3RCb3VuZGluZ0JveCIgeDE9IjAuNSIgeTE9IjAuMCIgeDI9IjAuNSIgeTI9IjEuMCI+PHN0b3Agb2Zmc2V0PSIwJSIgc3RvcC1jb2xvcj0iIzMzMzMzMyIvPjxzdG9wIG9mZnNldD0iMTAwJSIgc3RvcC1jb2xvcj0iIzAwMDAwMCIvPjwvbGluZWFyR3JhZGllbnQ+PC9kZWZzPjxyZWN0IHg9IjAiIHk9IjAiIHdpZHRoPSIxMDAlIiBoZWlnaHQ9IjEwMCUiIGZpbGw9InVybCgjZ3JhZCkiIC8+PC9zdmc+IA==');
  background: -webkit-gradient(linear, 50% 0%, 50% 100%, color-stop(0%, #333333), color-stop(100%, #000000));
  background: -moz-linear-gradient(#333333, #000000);
  background: -webkit-linear-gradient(#333333, #000000);
  background: linear-gradient(#333333, #000000);
}
body, body a {
  color: #cccccc;
}

h1.quote {
  -moz-transform: translate(-50%, -50%);
  -ms-transform: translate(-50%, -50%);
  -webkit-transform: translate(-50%, -50%);
  transform: translate(-50%, -50%);
  display: inline-block;
  vertical-align: middle;
  *vertical-align: auto;
  *zoom: 1;
  *display: inline;
  text-align: right;
  text-decoration: none;
  font-family: 'Oswald', sans-serif;
  font-weight: normal;
  position: absolute;
  top: 50%;
  left: 50%;
  font-size: 1.5em;
  line-height: 1.5em;
  margin: 0;
  text-shadow: 0 -1px 0  #ffffff, 0 2px 3px #000000;
}
h1.quote span {
  display: block;
}

.clouds {
  filter: progid:DXImageTransform.Microsoft.Alpha(Opacity=40);
  opacity: 0.4;
  pointer-events: none;
  position: absolute;
  overflow: hidden;
  top: 0;
  left: 0;
  right: 0;
  height: 100%;
}

.clouds-1,
.clouds-2,
.clouds-3 {
  background-repeat: repeat-x;
  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  height: 500px;
}
</style>

<h1 class='quote'>    
<span>你是个鬼魂，驾驶着一具用星尘做成的肉骨架。</span>    
<span>... 你害怕什么？</span>    
</h1>    
<div class='clouds'>    
<div class='clouds-1'></div>    
<div class='clouds-2'></div>    
<div class='clouds-3'></div>    
</div>    

<script>
(function(){function t(e,t){return[].slice.call((t||document).querySelectorAll(e))}if(!window.addEventListener)return;var e=window.StyleFix={link:function(t){try{if(t.rel!=="stylesheet"||t.hasAttribute("data-noprefix"))return}catch(n){return}var r=t.href||t.getAttribute("data-href"),i=r.replace(/[^\/]+$/,""),s=t.parentNode,o=new XMLHttpRequest,u;o.onreadystatechange=function(){o.readyState===4&&u()};u=function(){var n=o.responseText;if(n&&t.parentNode&&(!o.status||o.status<400||o.status>600)){n=e.fix(n,!0,t);if(i){n=n.replace(/url\(\s*?((?:"|')?)(.+?)\1\s*?\)/gi,function(e,t,n){return/^([a-z]{3,10}:|\/|#)/i.test(n)?e:'url("'+i+n+'")'});var r=i.replace(/([\\\^\$*+[\]?{}.=!:(|)])/g,"\\$1");n=n.replace(RegExp("\\b(behavior:\\s*?url\\('?\"?)"+r,"gi"),"$1")}var u=document.createElement("style");u.textContent=n;u.media=t.media;u.disabled=t.disabled;u.setAttribute("data-href",t.getAttribute("href"));s.insertBefore(u,t);s.removeChild(t);u.media=t.media}};try{o.open("GET",r);o.send(null)}catch(n){if(typeof XDomainRequest!="undefined"){o=new XDomainRequest;o.onerror=o.onprogress=function(){};o.onload=u;o.open("GET",r);o.send(null)}}t.setAttribute("data-inprogress","")},styleElement:function(t){if(t.hasAttribute("data-noprefix"))return;var n=t.disabled;t.textContent=e.fix(t.textContent,!0,t);t.disabled=n},styleAttribute:function(t){var n=t.getAttribute("style");n=e.fix(n,!1,t);t.setAttribute("style",n)},process:function(){t('link[rel="stylesheet"]:not([data-inprogress])').forEach(StyleFix.link);t("style").forEach(StyleFix.styleElement);t("[style]").forEach(StyleFix.styleAttribute)},register:function(t,n){(e.fixers=e.fixers||[]).splice(n===undefined?e.fixers.length:n,0,t)},fix:function(t,n,r){for(var i=0;i<e.fixers.length;i++)t=e.fixers[i](t,n,r)||t;return t},camelCase:function(e){return e.replace(/-([a-z])/g,function(e,t){return t.toUpperCase()}).replace("-","")},deCamelCase:function(e){return e.replace(/[A-Z]/g,function(e){return"-"+e.toLowerCase()})}};(function(){setTimeout(function(){t('link[rel="stylesheet"]').forEach(StyleFix.link)},10);document.addEventListener("DOMContentLoaded",StyleFix.process,!1)})()})();(function(e){function t(e,t,r,i,s){e=n[e];if(e.length){var o=RegExp(t+"("+e.join("|")+")"+r,"gi");s=s.replace(o,i)}return s}if(!window.StyleFix||!window.getComputedStyle)return;var n=window.PrefixFree={prefixCSS:function(e,r,i){var s=n.prefix;n.functions.indexOf("linear-gradient")>-1&&(e=e.replace(/(\s|:|,)(repeating-)?linear-gradient\(\s*(-?\d*\.?\d*)deg/ig,function(e,t,n,r){return t+(n||"")+"linear-gradient("+(90-r)+"deg"}));e=t("functions","(\\s|:|,)","\\s*\\(","$1"+s+"$2(",e);e=t("keywords","(\\s|:)","(\\s|;|\\}|$)","$1"+s+"$2$3",e);e=t("properties","(^|\\{|\\s|;)","\\s*:","$1"+s+"$2:",e);if(n.properties.length){var o=RegExp("\\b("+n.properties.join("|")+")(?!:)","gi");e=t("valueProperties","\\b",":(.+?);",function(e){return e.replace(o,s+"$1")},e)}if(r){e=t("selectors","","\\b",n.prefixSelector,e);e=t("atrules","@","\\b","@"+s+"$1",e)}e=e.replace(RegExp("-"+s,"g"),"-");e=e.replace(/-\*-(?=[a-z]+)/gi,n.prefix);return e},property:function(e){return(n.properties.indexOf(e)?n.prefix:"")+e},value:function(e,r){e=t("functions","(^|\\s|,)","\\s*\\(","$1"+n.prefix+"$2(",e);e=t("keywords","(^|\\s)","(\\s|$)","$1"+n.prefix+"$2$3",e);return e},prefixSelector:function(e){return e.replace(/^:{1,2}/,function(e){return e+n.prefix})},prefixProperty:function(e,t){var r=n.prefix+e;return t?StyleFix.camelCase(r):r}};(function(){var e={},t=[],r={},i=getComputedStyle(document.documentElement,null),s=document.createElement("div").style,o=function(n){if(n.charAt(0)==="-"){t.push(n);var r=n.split("-"),i=r[1];e[i]=++e[i]||1;while(r.length>3){r.pop();var s=r.join("-");u(s)&&t.indexOf(s)===-1&&t.push(s)}}},u=function(e){return StyleFix.camelCase(e)in s};if(i.length>0)for(var a=0;a<i.length;a++)o(i[a]);else for(var f in i)o(StyleFix.deCamelCase(f));var l={uses:0};for(var c in e){var h=e[c];l.uses<h&&(l={prefix:c,uses:h})}n.prefix="-"+l.prefix+"-";n.Prefix=StyleFix.camelCase(n.prefix);n.properties=[];for(var a=0;a<t.length;a++){var f=t[a];if(f.indexOf(n.prefix)===0){var p=f.slice(n.prefix.length);u(p)||n.properties.push(p)}}n.Prefix=="Ms"&&!("transform"in s)&&!("MsTransform"in s)&&"msTransform"in s&&n.properties.push("transform","transform-origin");n.properties.sort()})();(function(){function i(e,t){r[t]="";r[t]=e;return!!r[t]}var e={"linear-gradient":{property:"backgroundImage",params:"red, teal"},calc:{property:"width",params:"1px + 5%"},element:{property:"backgroundImage",params:"#foo"},"cross-fade":{property:"backgroundImage",params:"url(a.png), url(b.png), 50%"}};e["repeating-linear-gradient"]=e["repeating-radial-gradient"]=e["radial-gradient"]=e["linear-gradient"];var t={initial:"color","zoom-in":"cursor","zoom-out":"cursor",box:"display",flexbox:"display","inline-flexbox":"display",flex:"display","inline-flex":"display"};n.functions=[];n.keywords=[];var r=document.createElement("div").style;for(var s in e){var o=e[s],u=o.property,a=s+"("+o.params+")";!i(a,u)&&i(n.prefix+a,u)&&n.functions.push(s)}for(var f in t){var u=t[f];!i(f,u)&&i(n.prefix+f,u)&&n.keywords.push(f)}})();(function(){function s(e){i.textContent=e+"{}";return!!i.sheet.cssRules.length}var t={":read-only":null,":read-write":null,":any-link":null,"::selection":null},r={keyframes:"name",viewport:null,document:'regexp(".")'};n.selectors=[];n.atrules=[];var i=e.appendChild(document.createElement("style"));for(var o in t){var u=o+(t[o]?"("+t[o]+")":"");!s(u)&&s(n.prefixSelector(u))&&n.selectors.push(o)}for(var a in r){var u=a+" "+(r[a]||"");!s("@"+u)&&s("@"+n.prefix+u)&&n.atrules.push(a)}e.removeChild(i)})();n.valueProperties=["transition","transition-property"];e.className+=" "+n.prefix;StyleFix.register(n.prefixCSS)})(document.documentElement);
</script>

在线演示可能有问题，但是保存到本地是没问题的！