Every web developer had an experience where he test his web site on Chrome, IE and FireFox, to find out that the experience is a little bit different, because browsers have their own default implementation and rendering for the HTML elements.
Which means if you don't overwrite the default implementation with your own CSS rules, then the browser will use its own implementation.
If you are very keen on making the exact same user experience between all browsers even with the smallest details, then the community came up with a technique called "CSS Reset".
And even created a web site for that which you can find it on : CSS Reset Web Site Before you jump to add it into your code, we should mention some issues about it.
Many developers won't implement CSS Reset, because in most cases you are going to have your own rules for most of the HTML elements.
So, if you implement CSS Reset, or the ones the come by default, then you will be doing double work, because you are implementing a rule, then you override it, which means double processing time.
Adding to that, it might end up that the reset rules will override your desired rule, if the selectors for the reset rules where more specific than your desired rules.
But, in-spite of all these issues, it is an effort that worth doing.
In order to add CSS Reset, then you download the proper package that fits you from the CSS Reset Web Site and add it as the first link in your page.
Most probably, nowadays you are building HTML5 web sites, so make sure to download the HTML5 version of CSS Reset from HTML5 Doctor, or normalize CSS which is another implementation for HTML5.
If you are using a CSS framework, then most probably that framework has its own built-in CSS reset tool. For example bootstrap framework has its own CSS reset, which is called Reboot, which is based on normalize.