部分覆盖屏幕并滑动叠加元素 [英] Partial cover the screen and slide the overlay-element

问题描述

我尝试创建一个overlay-div，它覆盖整个屏幕 - 除了3em到底部。我认为我的尝试不是最佳的：

I try to create an overlay-div, which covers the whole screen - except 3em to the bottom. I think my attempt is not the optimum:

<div id="background"></div>
<div id="overlay"></div>

CSS ：

#background {
    background-color: #ddd;
    width: 100%;
    height: 100%;
}

#overlay {
    position: absolute;
    height: 100%;
    background-color: #fff;
    width: 100%;
    top: -3em;
    -webkit-box-shadow: 0px 3px 5px 0px rgba(0,0,0,0.3);
    -moz-box-shadow: 0px 3px 5px 0px rgba(0,0,0,0.3);
    box-shadow: 0px 3px 5px 0px rgba(0,0,0,0.3);
    z-index: 1;
}

这样，我想向上和向下滑动叠加。但是用上面的CSS，我不知道如何完全动画，因为'-55em'是太多的较低的屏幕分辨率或不够的更高的分辨率：

With that, I want to slide up and down the overlay. But with the css above, I don't know how to animate completely as '-55em' are too much on lower screen resolution or not enough on higher resolution:

JS：

JS:

$('#overlay').animate({'top':'-55em'}, 1000, function() {
    $('#overlay').animate({'top':'-3em'}, 1000);
});

推荐答案

我认为你应该改变高度，保存您的典型计算

i think you should change height instead of top it will save you from typical calculations

$('#overlay').animate({'height':'0%'}, 1000, function() {
	$('#overlay').animate({'height':'100%'}, 1000);
});

	#background {
		background-color: #ddd;
		width: 100%;
		height: 100%;
	}

	#overlay {
		position: absolute;
		height: 100%;
		background-color: #fff;
		width: 100%;
		top: -3em;
		-webkit-box-shadow: 0px 3px 5px 0px rgba(0,0,0,0.3);
		-moz-box-shadow: 0px 3px 5px 0px rgba(0,0,0,0.3);
		box-shadow: 0px 3px 5px 0px rgba(0,0,0,0.3);
		z-index: 1;
	}

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<div id="background"></div>
	<div id="overlay"></div>

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