Question about *correct* CSS Styling

Hello All,

Well my topic may seem a bit big and largely opinion based I was wondering 2 things.

Question A:

When I was styling a wordpress site for a client a while back I used quite a lot of margin-top etc. eventually it got to the point of having `margin-top: 85px;` and sometimes even more. Whilst this did not matter for the design as it was still responsive I wonderd if this was a good use of the property or if I should use another way.

Question B:

Kind of like the same thing as question A, however this time I was styling for specific width size's making the site responsive and all. But I think I made my code too specified or rather I was fighting my own code at a few times I think.

Example code:

@media only screen and (max-width: 320px) and (min-width: 251px) {
    div#logo img {
        width: 100%;
    }
 
    #content .site-wrapper .sidebar {
        float: left;
        width: 85%;
        padding-left: 20px;
    }
 
    body #content.withSidebar {
        width: 90%;
        float: left;
    }
}

Would this be correct or would you use another code? Ofcourse there is a `live` version (Still in development ATM)
The link is: http://grandbras.compar.nl/catering/ question A is also about this particular site.

I hope someone can help me with this. One could ofcourse say that this code would be correct since the site works and responsiveness does too but I want a more cleaner code. I have ofcourse looked through some tutorials but haven't found much to clean up my code. Any tips will be much appriated!

Thanks,
- RDAxRoadkill

//mod edit: BBCode tags added. Use [code] and [/code] tags around your html/css/js/php/etc. to maintain formatting. ~gt