Flexbox for mobile border width of 100% - html

Question

I'm using flexbox for my navigation and I can't seem to get my borders to work right for my media query specified for column wrap.
I want the borders to stretch across the device width completely, for example I want the border all the way from the left to all the way on the right on the device, and I want each a element to take up one 'row' on the device but currently the borders only stretch half way and some of the li elements are sharing a row when others are not and I'm not too sure why. Even when I make a to display block, it's not working. I also tried making flex basis 100% for the a elements.
Edit: I think I figured it out for the positioning. I made the #nav ul. not just #nav column wrap. However, I'm still experiencing the border problem unfortunately.
#nav {
display: -webkit-box;
display: -moz-box;
display: -ms-flexbox;
display: -webkit-flex;
display: flex;
-webkit-flex-flow: row wrap;
margin: 0;
flex-flow: row wrap;
justify-content: center;
align-items: center;
background-color: orange;
}
#nav li a {
color: white;
margin: 15px;
padding: 5px;
display: block;
;
text-decoration: none;
font-size: 24px;
font-family: courier;
}
#nav li {
list-style: none;
}
#nav ul {
display: -webkit-box;
display: -moz-box;
display: -ms-flexbox;
display: -webkit-flex;
display: flex;
-webkit-flex-flow: row wrap;
margin: 0;
flex-flow: row wrap;
justify-content: center;
align-items: center;
}
#media all and(max-width: 800px) {
#nav {
justify-content: space-around;
}
}
#media all and (max-width: 500px) {
#nav {
flex-flow: column wrap;
padding: 5px;
}
#nav li a {
flex: 1 100%;
display: block;
padding: 5px;
border-top: 1px solid black;
border-bottom: 1px solid black;
}
}
<div id="nav">
<ul>
<li> Calendar </li>
<li> Events </li>
<li> Hours </li>
<li> Contact </li>
<li> About </li>
</ul>
</div>

Answer 1

Try to reset the default padding on ul element.
ul {
padding-left: 0;
}
also reset the default margin on body if needed.
body {
margin: 0;
}
For the flexbox part, you should set display: flex; on #nav ul, rather than #nav. You don't need to set any style on #nav actually. If you want the each li to take 100% width in the media query, you can set flex item to flex: 1 1 100%;, working example in the fiddle below.
#media all and (max-width: 500px) {
#nav li {
flex: 1 1 100%;
padding: 5px;
border-top: 1px solid black;
border-bottom: 1px solid black;
}
}
jsFiddle