i would guess that your css declaration looks like this
<link rel="stylesheet" type="text/css" href="yourcss.css" />
<link rel="stylesheet" type="text/css" href="bootstrap.css" />
you should change them upside-down
<link rel="stylesheet" type="text/css" href="bootstrap.css" />
<link rel="stylesheet" type="text/css" href="yourcss.css" />
the reason is that any css that is closer to the body tag, will be considered the first priority. if items in yourcss.css has the SAME NAME with the items your bootstrap.css, the bootstrap.css's items will be OVERRIDDEN. if you didn't want to override these, make sure the item/class/id name is different for each in the yourcss.css. Make the best practice of giving each tag a different class name for your css.