调整响应导航栏图标/按钮的大小

Question

我正在尝试在我的学校项目网页中加入一个响应式导航栏，我希望导航栏中所有按钮的宽度为70px的倍数。

这是代码：

function myFunction() {
    var x = document.getElementById("myTopnav");
    if (x.className === "topnav") {
        x.className += " responsive";
    } else {
        x.className = "topnav";
    }
}

body {margin:0;}
ul.topnav {
  list-style-type: none;
  margin: 0;
  padding: 0;
  overflow: hidden;
  background-color: #333;
}

ul.topnav li {float: left;}

ul.topnav li a {
  display: inline-block;
  color: #f2f2f2;
  text-align: center;
  padding: 14px 16px;
  text-decoration: none;
  transition: 0.3s;
  font-size: 17px;
}

ul.topnav li a:hover {background-color:#556;
background-image: linear-gradient(30deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445),
linear-gradient(150deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445),
linear-gradient(30deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445),
linear-gradient(150deg, #445 12%, transparent 12.5%, transparent 87%, #445 87.5%, #445),
linear-gradient(60deg, #99a 25%, transparent 25.5%, transparent 75%, #99a 75%, #99a), 
linear-gradient(60deg, #99a 25%, transparent 25.5%, transparent 75%, #99a 75%, #99a);
background-size:80px 140px;
background-position: 0 0, 0 0, 40px 70px, 40px 70px, 0 0, 40px 70px;}

ul.topnav li.icon {display: none;}

@media screen and (max-width:745px) {
  ul.topnav li:not(:first-child) {display: none;}
  ul.topnav li.icon {
    float: right;
    display: inline-block;
  }
}

@media screen and (max-width:745px) {
  ul.topnav.responsive {position: relative;}
  ul.topnav.responsive li.icon {
    position: absolute;
    right: 0;
    top: 0;
  }
  ul.topnav.responsive li {
    float: none;
    display: inline;
  }
  ul.topnav.responsive li a {
    display: block;
    text-align: left;
  }
}

<ul class="topnav" id="myTopnav">
  <li><a class="active" href="#home">Home</a></li>
  <li><a href="#news">Phishing</a></li>
  <li><a href="#contact">Spamming</a></li>
  <li><a href="#about">Pharming</a></li>
  <li><a href="#about">Smishing</a></li>
  <li><a href="#about">Internet Protection</a></li>
  <li><a href="#about">Bibliography</a></li>
  <li class="icon">
    <a href="javascript:void(0);" style="font-size:15px;" onclick="myFunction()">☰</a>
  </li>
</ul>