相关疑难解决方法(0)

.container {
  width: 600px;
  height: 600px;
  background-color: salmon;
  position: relative;
  z-index: 99;
  margin-top: 20px;
  padding-top: 10px;
}

h1 {
  background-color: pink;
  position: relative;
  z-index: -1;
  font-family: monospace;
}

<div class="container">
  <h1>1. I can never be covered by parent if my z-index is positive.</h1>
  <h1>2. Even when my z-index is nagative, I still can never be covered if my parent has any z-index at all.</h1>
</div>

.main {
  font-family: 'Open Sans', Helvetica, sans-serif;
  display: flex;
  background-color: #99baef;
}

nav {
  height: 100%;
  width: 8em;
  background-color: black;
  z-index: 1;
}

.navbox {
  box-sizing: border-box;
  background-color: black;
  color: white;
  height: 4em;
  width: 100%;
  text-align: center;
  line-height: 4em;
  border-top: 1px dotted #99baef;
  transition: all 1s;
}

.navbox:hover {
  width: 130%;
  border-top: none;
  background-color: #4a77c4;
  color: black;
}

.container {
  padding: 1em;
}

a {text-decoration: inherit;}

<div class="main">
  <div class="maincolumn">
    <nav>
      <a href="">
        <div …

.wrapperRed {
  height: 200px;
  width: 200px;
  position: absolute;
  z-index: 1; /* Why is the red div in front of the green one, if this z-index is deleted? */
}

.red {
  position: absolute;
  height: 100%;
  width: 100%;
  background-color: red;
  z-index: 5;
}

.green {
  height: 200px;
  width: 200px;
  background-color: green;
  position: absolute;
  top: 100px;
  left: 100px;
  z-index: 1;
}

<div class="wrapperRed">
  <div class="red"></div>
</div>
<div class="green"></div>

body {
  padding: 30px;
}
.red1 {
  position: absolute;
  z-index: 1;
  width: 400px;
  height: 200px;
  background: red;
}
.red2 {
  position: absolute;
  z-index: 1;
  width: 400px;
  height: 200px;
  top: 250px;
  background: red;
}
.blue {
  z-index: 9;
  padding: 10px;
  text-align: center;
  color: white;
  text-transform: uppercase;
  position: absolute;
  top: 100px;
  left: 100px;
  width: 150px;
  height: 130px;
  background: blue;
}

<div class="red1">
  <div class="blue">
    blue child 1
  </div>
</div>
<div class="red2">
  <div class="blue">
    blue …

#fixed {
  background-color: red;
  width: 500px;
  height: 500px;
  position: fixed;
  z-index: 0;
}
#normal {
  background-color: blue;
  width: 500px;
  height: 500px;
  z-index: 1;
}

<div id = 'fixed'> I'm Fixed </div>
<div id = 'normal'> I'm Normal </div>