Not sure what you mean. but write up your own CSS with all your Size stuff and add !important after it and before the ;
Something like this:
.navbar-whatever {
whateverSizeCode = 0 !important;
whateverSizeCode2 = 0 !important;
}
Put Mobile tags for Twitter Bootstrap. Here is a link for you: http://getbootstrap.com/css/#overview-mobile
Mobile Code for you. Add this in your tag
<!-- Scroll Enabled -->
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- Scroll Disabled -->
<meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
Note: Use any one of the two lines.
Also make sure that in your HTML you do this:
<style rel="stylesheet" link="bootstrap.css">
<style rel="stylesheet" link="yourCSS.css">
What this will do is Put your styles and sizes in a way that Bootstrap is read by the code first then your CSS so that it does not override your CSS.
Hope so I Helped. Ask me again and be more specific.