Pixel Border and Percentage width in Proportion - css

Question

I think I might already know the answer to this one but I need a sanity check!
Say I have
#gridtest{
width:590px;
}
I could change the width to a percentage by using RESULT=TARGET/CONTEXT. In this case the context is a container with a max-width set to 1000px so I can do this:
#gridtestpercent{
width:59%; /*590/1000*/
}
If I were to shrink the window down the div would always be in the proportion to the its container. But what if I wanted to do
#gridtest{
width:570px;
border:10px solid red;
}
I can work the width out based on the target now being 570 but as the window is shrunk the proportions all go out of sync.
#gridtestpercentnoborder{
width:57%; /*570/1000*/
border:10px solid red;
}
I can't use percentage border. I don't want to use JS to keep checking the context and I can't use the CSS3 box-border declaration yet.
If I wanted to use the technique described in responsive web design by Ethan Marcotte where everything shrinks in relation to each other would I be out of luck if using a border?
Cheers!

Answer 1

You could use CSS3 calc() function,
.selector{
border: 5px solid black;
width: -moz-calc(50% - 10px);
width: -webkit-calc(50% - 10px);
width: calc(50% - 10px);
}
SASS mixin
#mixin calc($property, $expression) {
#{$property}: -moz-calc(#{$expression});
#{$property}: -webkit-calc(#{$expression});
#{$property}: calc(#{$expression});
}
article {
border: 1px solid red;
#include calc( width, '100% - 2px')
}

Answer 2

You could use an inset box-shadow instead of a border:
box-shadow: 0px 0px 0px 10px red inset;
Just pad the inside of the container to compensate.
Edit: I write "pad" but of course if you use padding it'll throw off the box dimensions. Margin the content inside instead.

Answer 3

The accepted answer is not correct. You actually have 2 options:
Use the box-sizing property, so all the paddings and borders are considered part of the size:
.column {
width: 16%;
float: left;
margin: 0 2% 0 2%;
background: #03a8d2;
border: 2px solid black;
padding: 15px;
font-size: 13px;
-webkit-box-sizing: border-box;
-moz-box-sizing: border-box;
box-sizing: border-box;
}
Or, use the outline property instead of the border property. You will still have problems with the paddings, but it's easier to add. Example:
.column {
width: 16%;
float: left;
margin: 0 2% 0 2%;
background: #03a8d2;
outline: 2px solid black;
}
Full explanation: http://designshack.net/articles/css/beating-borders-the-bane-of-responsive-layout/

Answer 4

Unfortunately, yes, you're out of luck. One hacky way to get around this problem is with a wrapper div that you use to create your border. So the outside div would be 57% (in your example) with a background that is the color of your desired border. Then, the inner div would have a width of 96% or so (play with the exact number to find a border that is appropriate for your design).

Answer 5

If you want to stay semantic you can use div { box-sizing:border-box; } or some absolutely positioned :after elements. See the post How do I add 1px border to a div whose width is a percentage?

Answer 6

In CSS3 you can also use the new box-sizing property to include the pixel and padding count into the width of the element:
box-sizing: border-box;

Answer 7

If possible, depending on your design, what I like to do is put the border as an absolute div with a width of 3px ( for example ) and a height higher than its parent div. I then set overflow hidden on the parent div.