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HTML - CSS - How to left-align images in a centered and resizable parent

I have a lot of thumbnails in my page: I want them to be centered, but the last line looks awful while resizing and I have something like one or two orphan images floating in the center of the page.
The last line should be left-aligned.
How to do it?
I tried to insert another div with "margin:0 auto 0 auto;" but it doesn't work.
https://jsfiddle.net/4hw4fkm9/
What I try to have:
<div style="text-align:center;">
<img />
<img />
<img />
<img />
etc..
</div>

You should use CSS for this, not the HTML attribute "align", which is pretty old school. You can either float the images left, in which case they will stack to the left, or you could set all the images to display: inline-block, then use text-align: center on their container element (the div in this case).
Here are some references:
http://www.w3schools.com/css/css_float.asp
http://www.w3schools.com/cssref/pr_class_display.asp

I'm not sure if this is what you're looking for - as you mention that you both 'want them centered' but want them left-aligned, too.
What you can do is create another div that will act as a container, set width: 100% on the main div, set the width slightly lower on the container div and set margin: 0 auto; on the container. Then make the images relatively positioned with left:0;.
See Updated Fiddle Here. Is this what you're after?
EDIT: Re-Updated Fiddle for my attached comment. You can use set pixel values on the main and container div to account for the set pixel width of the thumbnails + any spacing that occurs.

Using the selectors in the fiddle.
.center {
text-align:center;
background-color:red;
margin:0 auto;
padding:0 20px;
}
.center:after{
content:'';
display:table;
clear:both;
}
img {
width: 100px;
height: 100px;
float:left;
}
From there the .center element would need a width of some multiple of 100px to include a fixed number of imgs. I added padding to make it look closer to the picture you provided.

Alternate Column Position (Left & Right)

I have a list of post on a WordPress website that has an excerpt and an image. Each on in a column. One floated left, one floated right.
What I want to achieve is to alternate each post so that the first has a left aligned image, and right aligned text; then the second has a right aligned image and left aligned text, and then the next, left aligned image, right aligned text.
Perhaps there is a PhP or JS/Jquery way of doing this?
*Please see image so you can see what I mean.
There is also a basic HTML/CSS JSFiddle here: jsfiddle.net/huwrowlands/7WGTm/
Thanks

Now try to this
Used to pseudo-classes :nth-child(even) in your css define this in parents div as like this
.hp-module:nth-child(even) > .col:first-child{
float:right;
}
Demo
more about nth-child

CSS3 Pseudo (odd,even)
Using the new pseudo class :nth-child(odd) or :nth-child(even) it's very easy.
.hp-module {
width: 100%;
}
.col{
width: 46%;
padding: 2%;
float: right;
text-align: center;
}
.hp-module:nth-child(odd)>div{
float:left;
}
Demo
http://jsfiddle.net/7WGTm/3/

Overlaying one div over another, but not knowing the size of the div

I'm trying to lay one div over another. This is really simple if you know the dimensions of the div.
Solved here:
How to overlay one div over another div
So, here is my HTML:
<div class="container">
<div class="overlay"></div>
<div class="content"></div>
</div>
In my case, I don't know the exact dimensions of the "content" or "container" div. This is because I don't have control over any of the content in the div (we are making our app extensible for 3rd party developers).
See my example on jsFiddle
The overlay should cover the content entirely. Width 100% and Height 100%. However, this does not work because in my example I positioned the overlay absolutely.
One solution is to use JavaScript to get the size of the content div and then set the size of the overlay. I don't like this solution much since if image sizes are not specified, you need to wait until images are loaded and recalculate the size of the div.
Is there any way of solving this problem in CSS?

You could set the position to absolute and then set all 4 positioning values to 0px which will make the box expand. See a demo here: http://jsfiddle.net/6g6dy/
This way you dont have to worry about recalculating things if you want padding on the overlay or the container (like you would if you used actual height and width values), because its always going to be adjusted to the outer dimensions of the box.

It's not possible to do this because:
The overlay is not contained by anything to restrict it's size (since there is no height/width applied to the container).
The size of the content div can change as content loads (since it has no fixed width/height).
I solved this by using JavaScript*. Eg.
function resizeOverlay() {
$('.overlay').css({
width: $('.content').width()
height: $('.content').height()
});
}
$('.content').find('img').on('load', resizeOverlay);
*Code not tested.

Hey are you looking like this : http://tinkerbin.com/Vc4RkGgQ
CSS
.container {
position:relative;
background:blue;
color:white;
}
.content {
position:absolute;
top:0;
left:15px;
background:red;
color:yellow;
}

I do not know what you are exactly trying to do but this might work:
container must be relative: anything from static
overlay and content are absolute :move top/left in first non static parent; no flow.
Give same top/left to be on top and higher z-index for upper element.

See this demo: http://jsfiddle.net/rathoreahsan/kEsbx/
Are you trying to do as mentioned in above Demo?
CSS:
#container {
position: relative;
}
.overlay,
.content{
display:block;
position: absolute;
top: 0;
left: 0;
}
.overlay{
z-index: 10;
background: #ccc;
}

You can indeed do this without JavaScript. Your problem is that #container element has 100% width relative to the whole page. To fix this you can:
a) position it absolutely,
#container {
position: absolute;
}
b) make it float or
#container {
float: left;
}
c) make it display as table cell
#container {
display: table-cell;
}
One of the above is enough, you don't need to apply all. Also you should not position .content absolutely as this will prevent #container to have the same width/height.

If you are worried about images loading after the height is set you can go ahead and set the dimensions of the image in the containing div and use the padding-bottom hack. This way when the browsers paints over the page it knows how big the image will be before it loads.

Can the content remain centered while the screen size changes?

First, here's is my rough example: http://demindu.com/sandbox/simple.html
What I'm trying to do:
Create a content div: let's say 400px tall and 700px wide, like the example. The content box has a margin of 50px in each direction. The content div should always be centered both vertically and horizontally, regardless of screen resolution. The black background should extend from the centered content area all the way to the right side of the screen, but not to the left.
The only way I can think of possibly doing this is something using window.innerWidth & window.innerHeight in JavaScript, but I don't know enough to know if this is even possible.
The amount of blank space above and below the middle section would need to be:
window.innerHeight - height of the div (in this example: 500px [400px box with two 50px margins]) / 2
The blank space to the left of the black bar would need to be:
window.innerWidth - width of the div (in this example: 800px [700px box with two 50px margins]) / 2
My question to you is: Is this possible in JavaScript? Is this possible somehow with pure CSS?

You can do this entirely in CSS with 4-point absolute positioning. You will need two elements:
The first item spans from the right of the screen to the center where the content is positioned. This element uses absolute positioning for the top, left, and right coordinates of the element (we can leave bottom unspecified as it's taken care of by the height.)
The second item is nested in the former. This item has a fixed width to ensure the content itself remains in the specified width you've chosen. We can also set the height and padding on this object and the parent will inherit it's height. Don't use margins to simulate padding - it can cause cross browser issues when you're just trying to do some positioning tricks as we are here.
So your HTML code would look something like this:
<div id="my_centered_design">
<div id="my_centered_design_content">
<p>This is just some example text.</p>
</div>
</div>
And you're CSS would look like this:
div#my_centered_design {
background: #000;
margin-left: -400px;
margin-top: -250px;
left: 50%;
position: absolute;
right: 0;
top: 50%;
}
div#my_centered_design_content {
background: #333;
height: 400px;
/* I think you actually want padding for
the effect you're trying to accomplish */
padding: 50px;
width: 700px;
}
Essentially this is the same trick as the Joe2Tutorial except we are applying additional positioning rules to adhere the centered element to the right side of the screen.

I think this pure css solution would suit you best: http://www.joe2torials.com/view_tutorial.php?view=37

A very quick google resulted in this piece of code.
this code does not align a div in the middle. what you actually for your own website is that you put the following div css
.main {
width: 140px;background-color: #252525; float: left;margin-top: 25px; }
inside a table that is aligned to be centered. so, basically you're using the table's centering feature to center your left floated div simply as a content. you're not doing anything through div or css for that matter. the piece of css code you offered doesn't not anything about centering a div in the middle.

How can I center align a div without knowing the width?

I've looked this up and the outlook seems bleak. I'm not interested in using a table. I have 6 or so 'a element' inline-blocks that make up a menu. It's slick, except all the 'a elements' are set to width: auto; to accommodate their text. Without an explicit width, I'm not able to center align them. I have a container div and a child div that wraps around my 'a elements'.
Any thoughts?
Thanks
Mike

You could set the style of the a element to margin: 0 auto, but that doesn't work in IE6. In IE6, you should set the wrapper div to text-align: center, and (optionally) set the text-alignment for the a element back to text-align: left

<div style="width: auto; margin-left: auto; margin-right: auto">
div content
</div>
will align center on the page

the div element will take all the width space of the container element if it isn't set a width value.
So if you want to center a div you must set a width...
A solution to your problem (if I have understand it) can be:
<div style="text-align:center;"><span>[... yours content ...]</span></div>
where your div has became a span and a new div puts the span in the center.
Hope this can help you!
Bye,
Alberto

My advice is this answer - however someone commented that it wouldn't work in IE6. Here's how to make this work:
<div id="container">
<div id="centeredBlock">centered</div>
</div>
#container {
text-align: center;
}
#centeredBlock {
margin: 0 auto;
text-align: left;
width: 50%;
}

You need to set margin: 0 auto; on the outer container div, add text-align: center; on the inner div; and use an unordered list to build your menu in the first place.

Without setting an explicit width, the <div> tag will automatically expand to 100% of the width of its parent. Therefore, setting margin: 0 auto; will make it center -- with 0px on both the left and right.

here a nice workaround for centering a div with no width:
http://www.kensfi.com/how-to-align-center-a-div-with-no-width-declared/

Here is also a good example for the situation: http://www.cssplay.co.uk/menus/centered.html

If you need it centered and dynamically shrinking/expanding to accommodate the content without knowing the width, then your only option really is using a table. It is the only elastic element in HTML repertoire.
<table style="margin-left:auto;margin-right:auto;">
<tr>
<td>
Whatever...
</td>
</tr>
</table>
P.S. You can have a div to shrink dynamically as well by setting the float property to float:left or float:right. So it will stick to the left or the right, but you can't have it centered this way.