You could use box-shadow, possibly:

#something {
background: transparent url(https://i.stack.imgur.com/RL5UH.png) 50% 50% no-repeat;
min-width: 300px;
min-height: 300px;
box-shadow: inset 0 0 10px #0f0;
}

#something {
background: transparent url(https://i.stack.imgur.com/RL5UH.png) 50% 50% no-repeat;
min-width: 300px;
min-height: 300px;
box-shadow: inset 0 0 10px #0f0;
}

<div id="something"></div>

This has the advantage that it will overlay the background-image of the div, but it is, of course, blurred (as you'd expect from the box-shadow property). To build up the density of the shadow you can add additional shadows of course:

#something {
background: transparent url(https://i.stack.imgur.com/RL5UH.png) 50% 50% no-repeat;
min-width: 300px;
min-height: 300px;
box-shadow: inset 0 0 20px #0f0, inset 0 0 20px #0f0, inset 0 0 20px #0f0;
}

#something {
background: transparent url(https://i.stack.imgur.com/RL5UH.png) 50% 50% no-repeat;
min-width: 300px;
min-height: 300px;
box-shadow: inset 0 0 20px #0f0, inset 0 0 20px #0f0, inset 0 0 20px #0f0;
}

<div id="something"></div>

Edited because I realised that I'm an idiot, and forgot to offer the simplest solution first, which is using an otherwise-empty child element to apply the borders over the background:

#something {
background: transparent url(https://i.stack.imgur.com/RL5UH.png) 50% 50% no-repeat;
min-width: 300px;
min-height: 300px;
padding: 0;
position: relative;
}
#something div {
position: absolute;
top: 0;
left: 0;
right: 0;
bottom: 0;
border: 10px solid rgba(0, 255, 0, 0.6);
}

<div id="something">
<div></div>
</div>

Edited after @CoryDanielson's comment, below:

jsfiddle.net/dPcDu/2 you can add a 4th px parameter for the box-shadow that does the spread and will more easily reflect his images.

#something {
background: transparent url(https://i.stack.imgur.com/RL5UH.png) 50% 50% no-repeat;
min-width: 300px;
min-height: 300px;
box-shadow: inset 0 0 0 10px rgba(0, 255, 0, 0.5);
}

<div id="something"></div>

I don't know what you are comparing to.

But a super simple way to have a border look inset when compared to other non-bordered items is to add a border: ?px solid transparent; to whatever items do not have a border.

It will make the bordered item look inset.

http://jsfiddle.net/cmunns/cgrtd/

I would recomnend using box-sizing.

*{
-webkit-box-sizing:border-box;
-moz-box-sizing:border-box;
-ms-box-sizing:border-box;
box-sizing:border-box;
}


#bar{
border: 10px solid green;
}

To produce a border inset within an element the only solution I've found (and I've tried all the suggestions in this thread to no avail) is to use a pseudo-element such as :before

E.g.

.has-inset-border:before {
content: " "; /* to ensure it displays */
position: absolute;
left: 10px;
right: 10px;
top: 10px;
bottom: 10px;
border: 4px dashed red;
pointer-events: none; /* user can't click on it */
}

The box-sizing property won't work, as the border always ends up outside everything.

The box-shadow options has the dual disadvantages of not really working and not being supported as widely (and costing more CPU cycles to render, if you care).

If you want to make sure the border is on the inside of your element, you can use

box-sizing:border-box;

this will place the following border on the inside of the element:

border: 10px solid black;

(similar result you'd get using the additonal parameter inset on box-shadow, but instead this one is for the real border and you can still use your shadow for something else.)

Note to another answer above: as soon as you use any inset on box-shadow of a certain element, you are limited to a maximum of 2 box-shadows on that element and would require a wrapper div for further shadowing.

Both solutions should as well get you rid of the undesired 3D effects. Also note both solutions are stackable (see the example I've added in 2018)

.example-border {
width:100px;
height:100px;
border:40px solid blue;
box-sizing:border-box;
float:left;
}


.example-shadow {
width:100px;
height:100px;
float:left;
margin-left:20px;
box-shadow:0 0 0 40px green inset;
}


.example-combined {
width:100px;
height:100px;
float:left;
margin-left:20px;
border:20px solid orange;
box-sizing:border-box;
box-shadow:0 0 0 20px red inset;
}

<div class="example-border"></div>
<div class="example-shadow"></div>
<div class="example-combined"></div>

If box-sizing is not an option, another way to do this is just to make it a child of the sized element.

Demo

CSS

.box {
width: 100px;
height: 100px;
display: inline-block;
margin-right: 5px;
}
.border {
border: 1px solid;
display: block;
}
.medium { border-width: 10px; }
.large  { border-width: 25px; }

HTML

<div class="box">
<div class="border small">A</div>
</div>
<div class="box">
<div class="border medium">B</div>
</div>
<div class="box">
<div class="border large">C</div>
</div>

I know this is three years old, but thought it might be helpful to someone.

The concept is to use the :after (or :before) selector to position a border within the parent element.

    .container{
position:relative; /*Position must be set to something*/
}


.container:after{
position:relative;
top: 0;
content:"";
left:0;
height: 100%; /*Set pixel height and width if not defined in parent element*/
width: 100%;


-webkit-box-sizing:border-box;
-moz-box-sizing:border-box;
-ms-box-sizing:border-box;
box-sizing:border-box;


border:1px solid #000; /*set your border style*/


}

It's an old trick, but I still find the easiest way to do this is to use outline-offset with a negative value (example below uses -6px). Here's a fiddle of it—I've made the outer border red and the outline white to differentiate the two:

.outline-offset {
width:300px;
height:200px;
background:#333c4b;
border:2px solid red;
outline:2px #fff solid;
outline-offset:-6px;
}


<div class="outline-offset"></div>

You may use background-clip: border-box;

Example:

.example {
padding: 2em;
border: 10px solid rgba(51,153,0,0.65);
background-clip: border-box;
background-color: yellow;
}


<div class="example">Example with background-clip: border-box;</div>

So I was trying to have a border appear on hover but it moved the entire bottom bar of the main menu which didn't look all that good I fixed it with the following:

#top-menu .menu-item a:hover {
border-bottom:4px solid #ec1c24;
padding-bottom:14px !important;
}
#top-menu .menu-item a {
padding-bottom:18px !important;
}

I hope this will help someone out there.

Simple SCSS solution with pseudo-elements

Live demo: https://codepen.io/vlasterx/pen/xaMgag

// Change border size here
$border-width: 5px;


.element-with-border {
display: flex;
height: 100px;
width: 100%;
position: relative;
background-color: #f2f2f2;
box-sizing: border-box;
	

// Use pseudo-element to create inset border
&:before {
position: absolute;
content: ' ';
display: flex;
border: $border-width solid black;
left: 0;
right: 0;
top: 0;
bottom: 0;
border: $border-width solid black;
// Important: We must deduct border size from width and height
width: calc(100% - $border-width);
height: calc(100% - $border-width);
}
}

<div class="element-with-border">
Lorem ipsum dolor sit amet
</div>

You can do this:

.thing {
border: 2px solid transparent;
}
.thing:hover {
border: 2px solid green;
}

Simpler + better | img tag | z-index | link image | "alt" attribute

I figured out a method where you do not need to use the image as a background image but use the img HTML tag inside the div, and using z-index of the div as a negative value.

Advantages:

• The image can now become a link to a lightbox or to another page
• The img:hover style can now change image itself, for example: black/white to color, low to high opacity, and much more.
• Animations of image are possible The image is more accessible because of the alt tag you can use.
• For SEO the alt tag is important for keywords

#borders {
margin: 10px auto;
width: 300px;
height: 300px;
position:relative;
box-shadow: inset 0 0 0 10px rgba(0, 255, 0, 0.5);
}
img {
position:absolute;
top:0;
bottom:0;
left:0;
right: 0;
z-index: -1;
}

<div id="borders">
<img src="https://i.stack.imgur.com/RL5UH.png">
</div>