最简单的解决方案是让左边div的宽度等于100% -右边div的宽度加上它们之间的任何边距。

<div class="cont">
  <div class="search">
    Big Logo Text
  </div>
  <nav>
    <ul class="navbar">
      <li><a href="#1">NavLink1</a></li>
      <li><a href="#2">NavLink2</a></li>
      <li><a href="#3">NavLink3</a></li>
      <li><a href="#4">NavLink4</a></li>
      <li><a href="#5">NavLink5</a></li>
    </ul>
  </nav>
</div>

.cont{
  display: inline-grid;
  grid-template-columns: 160px 10px calc(100% - 170px);
  grid-template-rows: auto;
  grid-template-areas: "search .  navigation";
  width: 100%;
  height: auto;
  text-align: center;
}

.search {
  grid-area: search;
  height: 90px;
  background-color: #00FF00;
  line-height: 80px;
  font-size: 1.4rem;
  font-weight: 600;
}
nav {
  grid-area: navigation;
  height: 90px;
  background-color: #A53030;
}

.navbar{
  display: flex;
  height: 30px;
  width: 100%;
  padding: 0%;
  list-style-type: none;
  flex-flow: row wrap;
  flex: 0 1 auto;
  justify-content: space-between;
  align-content: flex-start;
  align-items: flex-start;
}

.navbar a{
    outline: 0;
    text-decoration: none;
}

https://codepen.io/tamjk/pen/dybqKBN

我想知道为什么没有人把position: absolute和position: relative放在一起使用

所以，另一个解决方案是:

HTML

<header>
  <div id="left"><input type="text"></div>
  <div id="right">Menu1 Menu2 Menu3</div>
</header>

CSS

header { position: relative;  }
#left {
    width: 160px;
    height: 25px;
}
#right {
    position: absolute;
    top: 0px;
    left: 160px;
    right: 0px;
    height: 25px;
}

Jsfiddle例子

使用显示:flex

<div style="width:500px; display:flex">
   <div style="width:150px; height:30px; background:red">fixed width</div>

   <div style="width:100%; height:30px; background:green">remaining</div>
</div>

我尝试了上面的解决方案，左边是液体，右边是固定的，但它们都不起作用(我知道这个问题是相反的，但我认为这是相关的)。以下是行之有效的方法:

.wrapper {margin-right:150px;}
.wrapper .left {float:left; width:100%; margin-right:-150px;}

.right {float:right; width:150px;}

<div class="wrapper"><div class="left"></div></div>
<div class="right"></div>

／* * css * /

#search {
 position: absolute;
 width: 100px;
}
.right-wrapper {
  display: table;
  width: 100%;
  padding-left:100px;
}
.right-wrapper #navigation {
 display: table-cell;
 background-color: #A53030;
}

／* * html * /

<div id="search"></div>
<div class="right-wrapper">
   <div id="navigation"></div>
</div>

如果您试图填充flexbox中2项之间的剩余空间，请将以下类添加到您想要分离的2项之间的空div:

.fill {
  // This fills the remaining space, by using flexbox. 
  flex: 1 1 auto;
}