Question

Is this valid CSS for browser reset? What does it do? I have been using this for a long time.

html,body,div,ul,ol,li,dl,dt,dd,h1,h2,h3,h4,h5,h6,pre,form,p,blockquote,fieldset,input,hr {margin:0; padding:0;}
h1,h2,h3,h4,h5,h6,pre,code,address,caption,cite,code,em,strong,th {font-size:1em; overflow:hidden; font-weight:normal; font-style:normal;}
ul,ol {list-style:none;}
fieldset,img,hr {border:none;}
caption,th {text-align:left;}
table {border-collapse:collapse; border-spacing:0;}
td {vertical-align:top;}

Answer 1

This is a version of Eric Meyer’s CSS reset. You can read about it here:
http://meyerweb.com/eric/thoughts/2011/01/03/reset-revisited/

The goal of a reset stylesheet is to reduce browser inconsistencies in
things like default line heights, margins and font sizes of headings,
and so on.

And here’s a history of why and how it came to life: http://sixrevisions.com/css/the-history-of-css-resets/