CSS - CSS3 pixelate dot background

Question 1

Here's the best I could come up with to match your image. It's adapted from the example here by Lea Verou What will be your fallback for non css3 browsers?

body {
    background-image: -moz-linear-gradient(45deg, #666 25%, transparent 25%), 
        -moz-linear-gradient(-45deg, #666 25%, transparent 25%), 
        -moz-linear-gradient(45deg, transparent 75%, #666 75%), 
        -moz-linear-gradient(-45deg, transparent 75%, #666 75%);
    background-image: -webkit-gradient(linear, 0 100%, 100% 0, color-stop(.25, #666), color-stop(.25, transparent)), 
        -webkit-gradient(linear, 0 0, 100% 100%, color-stop(.25, #666), color-stop(.25, transparent)), 
        -webkit-gradient(linear, 0 100%, 100% 0, color-stop(.75, transparent), color-stop(.75, #666)), 
        -webkit-gradient(linear, 0 0, 100% 100%, color-stop(.75, transparent), color-stop(.75, #666));
    background-image: -webkit-linear-gradient(45deg, #666 25%, transparent 25%), 
        -webkit-linear-gradient(-45deg, #666 25%, transparent 25%), 
        -webkit-linear-gradient(45deg, transparent 75%, #666 75%), 
        -webkit-linear-gradient(-45deg, transparent 75%, #666 75%);
    background-image: -o-linear-gradient(45deg, #666 25%, transparent 25%), 
        -o-linear-gradient(-45deg, #666 25%, transparent 25%), 
        -o-linear-gradient(45deg, transparent 75%, #666 75%), 
        -o-linear-gradient(-45deg, transparent 75%, #666 75%);
    background-image: linear-gradient(45deg, #666 25%, transparent 25%), 
        linear-gradient(-45deg, #666 25%, transparent 25%), 
        linear-gradient(45deg, transparent 75%, #666 75%), 
        linear-gradient(-45deg, transparent 75%, #666 75%);
    -moz-background-size: 2px 2px;
    background-size: 2px 2px;
    -webkit-background-size: 2px 2.1px; /* override value for webkit */
    background-position: 0 0, 1px 0, 1px -1px, 0px 1px;
}

jsfiddle example

Question 2

From thirtydot's comment in the first post. Should have posted it as an answer - Brilliant. I almost missed it. Please rate his comment up :) I am only posting this as an answer so it might help others as it helped me.

Using a base64 encoded message:

background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAYAAABytg0kAAAAGXRFWHRTb2Z0d2FyZQBBZG9iZSBJbWFnZVJlYWR5ccllPAAAABZJREFUeNpi2r9//38gYGAEESAAEGAAasgJOgzOKCoAAAAASUVORK5CYII=);

http://jsfiddle.net/thirtydot/v7T98/3/

Question 3

The "flickering" you observe is is not a software issue, but a hardware one. Basically, it's caused by that fact that the pixels on your screen can't change color instantly. Since your dotted background consists of alternating rows of pixels, any time you scroll down by an odd number of pixels, there will be a brief moment when your screen is switching between two shifted copies of the pattern, and this will appear as flicker.

This thread on Graphic Design Stack Exchange features an even more dramatic example of the same effect, and also explains why it happens in more detail. Just for a quick demonstration, let me borrow one of the images from Volker Siegel's answer:

Note how, on most screens, this image will show a noticeable "pulsing" effect when scrolled. (It may also appear to flicker a bit even while just looking at it, simply because the photoreceptors in your eyes also have some response delay and adaptation effects.)

Anyway, the only way you can stop your dotted background from flickering while scrolling is to make it not scroll. Fortunately, there's a CSS property just for that:

background-attachment: fixed;

Other than that, there's not much else to it. The best way to actually render the background is almost certainly with a simple two-color PNG image. You can even make the image semitransparent, so that you can layer it on top of different colored backgrounds. See the snippet below for a demonstration:

body {
  background-color: white;
  background-image: url(data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAABAAAAAQCAYAAAAf8/9hAAAAGUlEQVQ4y2NgoBJwoJAedcGoC0ZdMOAuAABF0hABJ/8lyQAAAABJRU5ErkJggg==);
  background-attachment: fixed;
}

<p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p>
<p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p>
<p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p>
<p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p><p>blah</p>

Note how the pattern does not flicker when you scroll it with the inner scroll bar. (It does flicker when you scroll the whole SO page, because the pattern is attached to the <iframe> it's displayed in, and will scroll along with it.)

^{(BTW, the inline image I've used in the snippet above is 16 × 16 pixels, even though the actual pattern is just 2 × 2 pixels. Repeating it a few times doesn't cost much in terms of file size, though, and might be slightly safer, as I seem to recall some older browsers having issues with very small background images.)}

Question 4

How about this one?

.card {
  background: linear-gradient(90deg, #fff 2px, transparent 1%) center, linear-gradient(#fff 2px, transparent 1%) center, #ccc;
  background-size: 5px 5px;
  
  height: 10em;
  width: 30em;
  position: relative;
}

.text {
  font-size: 2em;  
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}

<div class="card">
  <div class="text">
    Hello world!
  </div>
</div>

In general the formula is

// color
$bg-color: #fff;
$dot-color: $gray-darker;

// Dimensions
$dot-size: 3px;
$dot-space: 5px;

background: linear-gradient(90deg, $bg-color ($dot-space - $dot-size), transparent 1%) center,
linear-gradient($bg-color ($dot-space - $dot-size), transparent 1%) center, $dot-color;
background-size: $dot-space $dot-space;

as seen @ https://codepen.io/edmundojr/pen/xOYJGw

Question 5

This is because of background-size, so just try this:

background-size:2px 2px;

Question 6

Without all the browser prefixes:

background: linear-gradient(
    45deg,
    #fff,
    #fff 50%,
    #000 50%,
    #000
);
background-size: 2px 2px;