aligning a tag titles in a border

.main-header, .nav { 
display: flex;
flex-direction: column; 
align-self: center; 
}

.main-header h1, .nav li,
.nav li a { align-self: center; }

/* main header and navigation styles- base css*/ 

.nav li { 
list-style-type: none; 
display: block; 
border: solid 2px white; 
background-color: white; 
padding: 5px; 
margin-bottom: 10px; 
width: 70vw; 
margin-left: -10%;

} 

.nav li a{ 
text-decoration:none; 
color: black; 
text-align: center; 
margin: 0 auto;

}

<div id="wrapper">
<div id="header_info">
<header class="main-header"> 
<h1>Tracy Excell</h1>
 <ul class="nav">
      <li><a id="home">Home</a></li>
     <li><a href="#portfolio">Portfolio</a></li>
     <li><a href="#contact">Contact</a></li>
 </ul>

         <header>
            <a href="index.html">
                <h1>Tracy Excell</h1>
            </a>
            <nav class = 'container'>
                <ul>
                    <li><a href="index.html" class="selected">Home</a></li>
                    <li><a href="portfolio.html">Portfolio</a></li>
                    <li><a href="contact.html">Contact</a></li>
                </ul>
            </nav>
        </header>

        <div id="wrapper">

        </div>

.container {
   display: flex;
  flex-direction: column;
  flex-wrap: nowrap;   //your choice based on how you want it to wrap or not may not matter with a column lay out
  justify-content: center //this may not be necessary for a column, if you wanted your nav as a row then you need to pick
  align-content: center //has no effect when only one item on a line so may not be useful for a column nav
}

nav {
   text-align: center;   //will align your text to center
   padding: 10px 0;  // will give some padding on whole nav bar
    margin: 15px 0;  // will give some space between top and bottom of the actual nav bar
   font-size: 1.55em; //you can give your font a fixed or relative unit
  background: #000; //give your nav color  
  color: #fff;  //give text color
}

nav ul {
  list-style: none;   //will remove any unwanted styles 
  margin: 0 20px;  //this is if you want to target margins of actual unordered list, this is the box inside the nav box.
}

nav li {
  padding: .15em   //this gives the individual list items a bit of padding
  margin: .20em // this gives space between individual nave items
}

nav a {
    padding: 5px 30px; //this gives the actual words within your nav a larger clickable area which is important.
}