在 div 顶部停止关键帧动画？

Question

我在我的 404 页面上使用 this fun scrolling text effect，但我需要停止（短）文本并在它到达页面顶部时保持可见，而不是一直向上滚动。如何仅使用 CSS 实现这一点？我想尽量少用js。

Answer 1

我稍微破坏了代码库，但基本上你想从slide 动画中删除infinite iteration count 并在其位置添加forward（这是一个fill mode）。然后你想用top: 0% 替换动画中的top 值。最后，您想要移除#titles:after 上的黑色渐变，这可以通过完全移除或降低其不透明度来完成。仍然需要工作，但这是总体思路（必须以“全页”模式运行）：

@import url(http://fonts.googleapis.com/css?family=Droid+Sans:400,700);

* { padding: 0; margin: 0; }

body, html
{
	width: 100%;
	height: 100%;
	font-family: "Droid Sans", arial, verdana, sans-serif;
	font-weight: 700;
	color: #ff6;
	background-color: #000;
	overflow: hidden;
}

p#start
{
	position: relative;
	width: 16em;
	font-size: 200%;
	font-weight: 400;
	margin: 20% auto;
	color: #4ee;
	opacity: 0;
	z-index: 1;
	-webkit-animation: intro 2s ease-out;
	-moz-animation: intro 2s ease-out;
	-ms-animation: intro 2s ease-out;
	-o-animation: intro 2s ease-out;
	animation: intro 2s ease-out;
}

@-webkit-keyframes intro {
	0% { opacity: 1; }
	90% { opacity: 1; }
	100% { opacity: 0; }
}

@-moz-keyframes intro {
	0% { opacity: 1; }
	90% { opacity: 1; }
	100% { opacity: 0; }
}

@-ms-keyframes intro {
	0% { opacity: 1; }
	90% { opacity: 1; }
	100% { opacity: 0; }
}

@-o-keyframes intro {
	0% { opacity: 1; }
	90% { opacity: 1; }
	100% { opacity: 0; }
}

@keyframes intro {
	0% { opacity: 1; }
	90% { opacity: 1; }
	100% { opacity: 0; }
}

h1
{
	position: absolute;
	width: 2.6em;
	left: 50%;
	top: 25%;
	font-size: 10em;
	text-align: center;
	margin-left: -1.3em;
	line-height: 0.8em;
	letter-spacing: -0.05em;
	color: #000;
	text-shadow: -2px -2px 0 #ff6, 2px -2px 0 #ff6, -2px 2px 0 #ff6, 2px 2px 0 #ff6;
	opacity: 0;
	z-index: 1;
	-webkit-animation: logo 5s ease-out 2.5s;
	-moz-animation: logo 5s ease-out 2.5s;
	-ms-animation: logo 5s ease-out 2.5s;
	-o-animation: logo 5s ease-out 2.5s;
	animation: logo 5s ease-out 2.5s;
}

h1 sub
{
	display: block;
	font-size: 0.3em;
	letter-spacing: 0;
	line-height: 0.8em;
}

@-webkit-keyframes logo {
	0% { -webkit-transform: scale(1); opacity: 1; }
	50% { opacity: 1; }
	100% { -webkit-transform: scale(0.1); opacity: 0; }
}

@-moz-keyframes logo {
	0% { -moz-transform: scale(1); opacity: 1; }
	50% { opacity: 1; }
	100% { -moz-transform: scale(0.1); opacity: 0; }
}

@-ms-keyframes logo {
	0% { -ms-transform: scale(1); opacity: 1; }
	50% { opacity: 1; }
	100% { -ms-transform: scale(0.1); opacity: 0; }
}

@-o-keyframes logo {
	0% { -o-transform: scale(1); opacity: 1; }
	50% { opacity: 1; }
	100% { -o-transform: scale(0.1); opacity: 0; }
}

@keyframes logo {
	0% { transform: scale(1); opacity: 1; }
	50% { opacity: 1; }
	100% { transform: scale(0.1); opacity: 0; }
}

/* the interesting 3D scrolling stuff */
#titles
{
	position: absolute;
	width: 18em;
	height: 10em;
	bottom: 0;
	left: 50%;
	margin-left: -9em;
	font-size: 350%;
	text-align: justify;
	overflow: hidden;
	-webkit-transform-origin: 50% 100%;
	-moz-transform-origin: 50% 100%;
	-ms-transform-origin: 50% 100%;
	-o-transform-origin: 50% 100%;
	transform-origin: 50% 100%;
	-webkit-transform: perspective(300px) rotateX(25deg);
	-moz-transform: perspective(300px) rotateX(25deg);
	-ms-transform: perspective(300px) rotateX(25deg);
	-o-transform: perspective(300px) rotateX(25deg);
	transform: perspective(300px) rotateX(25deg);
}

#titles:after
{
	position: absolute;
	content: ' ';
	left: 0;
	right: 0;
	top: 0;
	bottom: 60%;
	background-image: -webkit-linear-gradient(top, rgba(0,0,0,0.5) 0%, transparent 100%);
	background-image: -moz-linear-gradient(top, rgba(0,0,0,0.5) 0%, transparent 100%);
	background-image: -ms-linear-gradient(top, rgba(0,0,0,0.5) 0%, transparent 100%);
	background-image: -o-linear-gradient(top, rgba(0,0,0,0.5) 0%, transparent 100%);
	background-image: linear-gradient(top, rgba(0,0,0,0.5) 0%, transparent 100%);
	pointer-events: none;
}

#titles p
{
	text-align: justify;
	margin: 0.8em 0;
}

#titles p.center
{
	text-align: center;
}

#titles a
{
	color: #ff6;
	text-decoration: underline;
}

#titlecontent
{
	position: absolute;
	top: 100%;
  width: 100%;
	-webkit-animation: scroll 10s linear 4s forwards;
	-moz-animation: scroll 10s linear 4s forwards;
	-ms-animation: scroll 10s linear 4s forwards;
	-o-animation: scroll 10s linear 4s forwards;
	animation: scroll 10s linear 4s forwards;
}

/* animation */
@-webkit-keyframes scroll {
	0% { top: 100%; }
	100% { top: 0% }
}

@-moz-keyframes scroll {
	0% { top: 100%; }
	100% { top: 0% }
}

@-ms-keyframes scroll {
	0% { top: 100%; }
	100% { top: 0% }
}

@-o-keyframes scroll {
	0% { top: 100%; }
	100% { top: 0% }
}

@keyframes scroll {
	0% { top: 100%; }
	100% { top: 0% }
}

<p id="start">A short time ago in a browser very, very close&hellip;</p>

<h1>STAR WARS<sub>titles in CSS3</sub></h1>

<div id="titles"><div id="titlecontent">

	<p class="center">ERROR 404</p>
	
	<p class="center">Page not found</p>
</div></div>