HR tag for horizontal line is not working

[rachell]

I can't figure out why my \[code\]<hr>\[/code\] styling is not working. Basically I want just a horizontal black line separating my elements.Here is my websiteCSS\[code\]/* Horizontal Line */.line_break { width:1000px; height: 5px; float: left; color: black; padding-top: 3px; background-color: rgba(255,255,255,.5);}\[/code\]HTML\[code\]<!---Navigation Menu ______________________________________________--> <div id="main_menu" class="wrapper_nav_box"> <div class="nav_box"> <a href="http://stackoverflow.com/questions/15582729/writing.html">WRITING</a> </div> <div class="nav_box"> <a href="http://tumblr.com">BLOG</a> </div> <div class="nav_box"> <a href="http://stackoverflow.com/questions/15582729/contact.html">CONTACT</a> </div> </div> <hr class="line_break">\[/code\]If you zoom in, you'll see that there's a weird border on the left hand side. I've tried messing around with height, but it never changes.