The PHP way is very easy. You just need a few things running:
Your server must allow you to use PHP
Your files must not have an .html extension, instead you must use .php
Create an external file with the code you want in.
In your actual file, place this line of code where you want your inserted code to be (in the example the external file is called “header.php”).
<?php include ("header.php");?>
That’s all.
If you don’t want to use programming you can still update your header in multiple files. You can use a free editor like Notepad++ and in the search menu use the “search in files” tool. It can look and replace code in several documents at a time.
There are other ways to do it, like using SSI or templates, but I guess this two are good options for you.
About the gaps between elements in IE, there must be none. Just remember every browser uses it’s own default CSS. A common technique is to clear all margins and paddings for every HTML tag (headers, list, paragraphs, etc.) Do it in your first rule and then define again for each one. This way you’ll have control over all of your margin elements and it will be consistent in all browsers. Of course there are bugs with double margins in old IE and other issues, but you’ll reduce the options if you start this way.
I hope this helps
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