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Protect element from global css

My js is embedded on a third party website and it creates an <iframe> which contains a simple comments panel , but apparently on this specific website there is a CSS stylesheet which styles every <iframe> tag in the dom with the !important flag , so i can't change those css rules and the website dev team won't change this behaviour, there is another way to overcome this? can i change the tagname and still be an iframe? anything?

You can use the all property with the initial value to default the styles for that element.
From the docs:
The all CSS shorthand property sets all of an element's properties
(other than unicode-bidi and direction) to their initial or inherited
values, or to the values specified in another stylesheet origin.
A code example:
#div-to-reset-styles {
all: initial;
* {
all: unset;
}
}
Just target your specific iframe and you should be fine.

CSS Specificity is your friend here. From this overview:
Specificity determines, which CSS rule is applied by the browsers.
Specificity is usually the reason why your CSS-rules don’t apply to some elements, although you think they should.
Every selector has its place in the specificity hierarchy.
If two selectors apply to the same element, the one with higher specificity wins.
There are four distinct categories which define the specificity level of a given selector: inline styles, IDs, classes, attributes, and elements.
...
The part in bold means that you can add a class to your element(s) in question and override the more generic iframe css definition like that.

How to make an element's CSS NOT inherit from others?

I want the element to use only css that are in the "A" section and ignore the "B" section.
Is it possible?If javascript can do this, How?
Thanks you.

You can not do that with the example you've provided. The C in CSS stands for Cascading, the styling rules cascade down the DOM tree.
You have to reset the styling of the element to what you want with a more specific selector, e.g. #Examplewrapper input{}. By using a more specific selector, it'll overwrite/suplement the previous styling, without the need for !important.
Alternatively, you can set the most upper selector more specific, e.g. #content input{}. This way, when you place a form in the #footer, it will not have the styling, as #content doesn't have a #footer in it (it cant cascade).
I do recommend to define a general input as you have. This way, all forms have the same font, size and styling throughout your website. If you want another color border, you only have to change that one settings. This is the way many (profesional) sites work, because it is the most efficient.

This is how the inheritance works. You can only overwrite styles if others are set globally (i.e. for all input elements).
You can always limit the global styles of input with some classname, like input.myStyle so the raw input will have no styles set.

Moving an element into a new div - doesn't take on its new css properties

So, I have an element that has some "pre-existing" behavior attached to it. So, I found that just moving it (as required by some new requirements) retains the existing behaviors = good. But the issue is, when I move the element I need to give it "new styles".
So, if I have something like this:
<div id="existingStructure">
<div id="legacyElement"></div>
</div>
Now, that has pre-existing styles attached to both. I can rearrange these styles etc.. but I can't change them. The styles are attached to the "id's" rather than a class definition. I believe I can change that if needed.
Now, I need to move "legacyElement" when certain things happen to a "new div".
I just
jQuery('#newStructure').append('#legacyElement');
<div id="newStructure">
<div id="legacyElement"></div>
</div>
Unfortunetly, the styles I have on newStructure don't seem to be applying to *legacyElement" when it gets moved here dynamically.
I was thinking of moving all the styles to a class rather than associated to the ids, and when I move it.. I just jQuery().addClass / jQuery().removeClass etc...
Is there a better/easier more robust way that I can just have the legacyElement loose its styles when it sits under existingStructure and then get new ones when moved to "newStructure" etc.. and vice versa. That element "legacyElement" will be pinging back and forth.. so, I need it to have the styles under each parent div as it goes there.
so when an action happens on page, I move it back:
jQuery('#existingStructure').append('#legacyElement');
If I am not succinct enough, please let me know.
The EXISTING styles are in an external CSS file and are like so..
#existingStructure {
// bunch of css
}
#existingStructure .item1 input[type="text"] {
// bunch of css
}
#legacyElement{
// bunch of css
}
and new styles are sorta the same except 'additional styles' might be applied.
#newStructure {
// bunch of css
}
#newStructure .item1 input[type="text"] {
// bunch of css
}

You can certainly target your div styles by their parents:
#existingStructure #legacyElement {some styles}
#newStructure #legacyElement {some other styles}
To explain futher, this arrangement should result in greater specificity, overriding styles that are simply applied to either #existingStructure or #legacyElement. I'm hoping no one did anything foolish like using !important on them.

Short answer: It should.
Here's an example I quickly made in jsFiddle: http://jsfiddle.net/CCm4J/1/
So then why isn't yours? Most likely you have css rules that are embedded that apply only when in the existingStructure id/class perhaps? Without see more of your css I'm not sure how specific I can get. I would just verify that your css rules are allowed to apply outside of existingStructure (and even that existingStructure might have rules for its parent too!)

Change CSS properties of non-existing elements

I want to change the dimensions of a set of elements that are not created yet. They will be created by a JavaScript script that I don't have access to. JQuery's css() function would apply the changes only on existing items, while I want the code to work like if I had set CSS properties in a CSS file.
Can anyone help me do it?

One option would be to dynamically create a style element:
$("<style type='text/css'> .redbold{ color:#f00; font-weight:bold;} </style>").appendTo("head")
$("<div/>").addClass("redbold").appendTo("body");
Taken from here: Create a CSS rule / class with jQuery at runtime.
Here's a possible IE alternative (see Creating a CSS class in jQuery):
document.styleSheets[0].addRule('body', 'background: green', -1);
For reference, see the documentation for addRule.

How to apply function to all elements having border-radius property

The idea is making some border-radius effect in IE 7/8, so I've decided to use jquery.corner.js library. To make it more generic I want to write some script which applies corner() function to all elements within a page having border-radius property.
For example, for this element
.someElement
{
border-radius:10px;
}
function must do the following
$(".someElement").corner("10px");
The problem is that I want to apply rounded corners to all elements, including dynamically added elements and elements which are inheriting border-radius property among some action(hover, click, etc.). Is this possible?

You need to declare a function that applies you css on every change.
To detect css style changes, see here:
Event detect when css property changed using Jquery
Then you need call that function on style change and on dom tree change (every time you append something into the page)....
I would advise you use a specific class to apply border radius css. This way you can select the rounded elements via jQuery class selectors.

You should have a generic css class that is used on all elements that have rounded borders and then use that class in your selector.
You will have to do this in a document ready handler. This will of course only apply rounded borders to elements that currently exists. If you want to cover elements loaded with ajax you can do the following:
$(document).ajaxSuccess(function(e, xhr, settings)
{
$(xhr.responseText).find(".class-that-applies-rounded-borders").corner("10px");
});