CSS: Setting width/height as Percentage minus pixe

I've seen this question asked in a couple other contexts on SO, but I thought it would be worth asking again for my particular case. I'm trying to create some re-usable CSS classes for more consistency and less clutter on my site, and I'm stuck on trying to standardize one thing I use frequently.

I have a container div that I don't want to set the height for (because it will vary depending on where on the site it is), and inside it is a header div, and then an unordered list of items, all with CSS applied to them. It looks a lot like this:

Widget

I want the unordered list to take up the remaining room in the container div, knowing that the header div is 18px tall. I just don't know how to specify the list's height as "the result of 100% minus 18px". Does anyone have any advice in this situation?

标签： css height pixels

11条回答

心情的温度

2楼-- · 2019-01-01 16:59

I tried some of the other answers, and none of them worked quite how I wanted them to. Our situation was very similar where we had a window header and the window was resizable with images in the window body. We wanted to lock the aspect ratio of the resizing without needing to add in calculations to account for the fixed size of the header and still have the image fill the window body.

Below I created a very simple snippet that shows what we ended up doing that seems to work well for our situation and should be compatible across most browsers.

On our window element we added a 20px margin which contributes to positioning relative to other elements on the screen, but does not contribute to the "size" of the window. The window-header is then positioned absolutely (which removes it from the flow of other elements, so it won't cause other elements like the unordered list to be shifted) and its top is positioned -20px which places the header inside of the margin of the window. Finally our ul element is added to the window, and the height can be set to 100% which will cause it to fill the window's body (excluding the margin).

*,*:before,*:after
{
  box-sizing: border-box;
}

.window
{
  position: relative;
  top: 20px;
  left: 50px;
  margin-top: 20px;
  width: 150px;
  height: 150px;
}

.window-header
{
  position: absolute;
  top: -20px;
  height: 20px;
  border: 2px solid black;
  width: 100%;
}

ul
{
  border: 5px dashed gray;
  height: 100%;
}

<div class="window">
  <div class="window-header">Hey this is a header</div>
  <ul>
    <li>Item 1</li>
    <li>Item 2</li>
    <li>Item 3</li>
    <li>Item 4</li>
    <li>Item 5</li>
  </ul>
</div>

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时光乱了年华

3楼-- · 2019-01-01 17:01

Thanks, i solved mine with your help, tweaking it a little since i want a div 100% width 100% heigth (less height of a bottom bar) and no scroll on body (without hack / hiding scroll bars).

For CSS:

 html{
  width:100%;height:100%;margin:0px;border:0px;padding:0px;
 }
 body{
  position:relative;width:100%;height:100%;margin:0px;border:0px;padding:0px;
 }
 div.adjusted{
  position:absolute;width:auto;height:auto;left:0px;right:0px;top:0px;bottom:36px;margin:0px;border:0px;padding:0px;
 }
 div.the_bottom_bar{
  width:100%;height:31px;margin:0px;border:0px;padding:0px;
}

For HTML:

<body>
<div class="adjusted">
 // My elements that go on dynamic size area
 <div class="the_bottom_bar">
  // My elements that goes on bottom bar (fixed heigh of 31 pixels)
 </div>  
</div>

That did the trick, oh yes i put a value little greatter on div.adjusted for bottom than for bottom bar height, else the vertical scrollbar appears, i adjusted to be the nearest value.

That difference is because one of the elements on dynamic area is adding an extra bottom hole that i do not know how to get rid of... it is a video tag (HTML5), please note i put that video tag with this css (so there is no reason for it to make a bottom hole, but it does):

 video{
  width:100%;height:100%;margin:0px;border:0px;padding:0px;
 }

The objetive: Have a video that takes the 100% of the brower (and resizes dynamically when browser is resized, but without altering the aspect ratio) less a bottom space that i use for a div with some texts, buttons, etc (and validators w3c & css of course).

EDIT: I found the reason, video tag is like text, not a block element, so i fixed it with this css:

 video{
  display:block;width:100%;height:100%;margin:0px;border:0px;padding:0px;
 }

Note the display:block; on video tag.

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步步皆殇っ

4楼-- · 2019-01-01 17:03

I realise this is an old post, but given that it hasn't been suggested it is worth mentioning that if you are writing for CSS3-compliant browsers, you can use calc:

height: calc(100% - 18px);

It's worth it to note that not all browsers currently support the standard CSS3 calc() function, so implementing the browser specific versions of the function may be required like the following:

/* Firefox */
height: -moz-calc(100% - 18px);
/* WebKit */
height: -webkit-calc(100% - 18px);
/* Opera */
height: -o-calc(100% - 18px);
/* Standard */
height: calc(100% - 18px);

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像晚风撩人

5楼-- · 2019-01-01 17:03

Don't define the height as a percent, just set the top=0 and bottom=0, like this:

#div {
   top: 0; bottom: 0;
   position: absolute;
   width: 100%;
}

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不流泪的眼

6楼-- · 2019-01-01 17:04

I'm not sure if this work in your particular situation, but I've found that padding on the inside div will push content around inside of a div if the containing div is a fixed size. You would have to either float or absolutely position your header element, but otherwise, I haven't tried this for variable size divs.

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呛了眼睛熬了心

7楼-- · 2019-01-01 17:06

Use negative margins on the element you would like to minus pixels off. (desired element)
Make overflow:hidden; on the containing element
Switch to overflow:auto; on the desired element.

It worked for me!

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