如何使内部div拉伸到100％的宽度？

Question

I have one header , and two div elements. The outer div is vertically centered in my header element. I want the inner div to stretch to 100% width. How do i do this?

Check this fiddle for reference. I want the blue section to take up 100 % of the total width.

Here's the code aswell:

HTML:

<header id="header-index">
    <div id="header-index-inner">
        <div id="inner-div">

                <h1>Header</h1>               
                <h5>Subheader1 </h5>
                <h5>Subheader2 </h5>

        </div>
    </div>
</header>

CSS:

#header-index{    
    background-color: red;
}

#header-index-inner{   
    width: 100%;
    display: table-cell;
    vertical-align: middle;
    height: 400px;
}

#inner-div{
  background-color:blue;
  width:100%;
}

Answer 1

Add the following to the #header-index rule:

display:table;
width:100%;

Answer 2

The issue is that #header-index-inner is display: table-cell , and it is not stretching 100%.

The parent needs to be assigned display: table , as well as width 100%:

#header-index {    
    background-color: red;
    display: table;
    width: 100%;
}

#header-index-inner {   
    width: 100%;
    display: table-cell;
    vertical-align: middle;
    height: 400px;
}

#inner-div{
  background-color:blue;
  width:100%;
}

Updated Fiddle

Answer 3

Instead of changing the display to use tables and table cells, you can use positioning to center the inner div with:

 #header-index { background-color: red; } #header-index-inner { width: 100%; height: 400px; } #inner-div { background-color: blue; top: 50%; position: relative; transform: translate(0%, -50%); } 

 <header id="header-index"> <div id="header-index-inner"> <div id="inner-div"> <h1>Header</h1> <h5>Subheader1 </h5> <h5>Subheader2 </h5> </div> </div> </header>