"over-ruling" definitions in CSS

I'm still new to CSS, but this struck me as odd:

if i have in my CSS:

img { border: none}

noborder {boder:none}


______

Now, if in the html i make a div class=noborder, the image in this div will still have a border... is there any way of "over-ruling" prior definitions that I'm missing?

Thanks, Matt

well, i believe thats cuz noborder needs a . before it

sorry, that was a typo

here is the exact prob im having now. im assuming its a simple solution, but im pretty confuddeled:

img {
border: solid white 1px;
}

.imgdown{
border: yellow;
}
<div class="imgdown">

<img src="http://www.asdfpics/yourguide.jpg" alt= ski>

</div>

______

This does not make the border yellow, and something even stranger is when i put border: yellow solid 1px; then a yellow border does appear, but completely not the right size and this whole thing is tripping me out:SSSS

matt

try


or if u don't want the border


addin the img there lets you control all imgs contained in the div with class=imgdown