Set the width of children to fill the parent

Question

I want the children of the div fill its width.

now am using a code like this:

.parent {
  width: 100%;
  display: inline-block;
  height: 120px;
  background: #000;
  padding: 10px;
  box-sizing: border-box;
}

.child {
  display: inline-block;
  margin-left: 1%;
  width: 31.4%;
  height: 100px;
  background: #ddd;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>

and it's working for 3 boxes, but what I want is that - Even if the box count is one or two i want them to fill the parent width. I want to achieve this using only CSS.

Answer 1

You can achieve this using flexbox properties.

Here is a demo:

.parent {
  display: flex;
  height: 120px;
  background: #000;
  padding: 10px;
  box-sizing: border-box;
}

.child {
  height: 100px;
  background: #ddd;
  flex: 1;
  margin: 0 10px;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
</div>

<div class="parent">
  <div class="child"></div>
</div>

Answer 2

You can make the parent a flexbox and define for the children to grow when there is space available. I removed the width for .child.

.parent {
  width: 100%;
  display: inline-flex;
  height: 120px;
  background: #000;
  padding: 10px;
  box-sizing: border-box;
}

.child {
  display: inline-block;
  margin-left: 1%;
  height: 100px;
  background: #ddd;
  flex-grow: 1;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
</div>

<div class="parent">
  <div class="child"></div>
</div>

Answer 3

Use flexbox:

.parent {
  width: 100%;
  display: flex;
  background: #000;
  padding: 10px;
  box-sizing: border-box;
  margin-bottom: 15px;
}

.child {
  flex: 1;
  margin: 0 10px;
  height: 100px;
  background: #ddd;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>
</div>

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
</div>

<div class="parent">
  <div class="child"></div>
</div>

Answer 4

You are using width like 30% which is fixed for every element, so every time you create other element its size is fixed and added at the end of residing elements and after total width is more than that of parent container it overflows.

Instead use flex-box.

.parent {
  width: 100%;
  display:flex;
  height: 120px;
  background: #000;
  padding: 10px;
  box-sizing: border-box;
}

.child {
  flex:1;
  margin-left: 1%;
  width: 31.4%;
  height: 100px;
  background: #ddd;
}

<div class="parent">
  <div class="child"></div>
  <div class="child"></div>
  
  <div class="child"></div>
  <div class="child"></div>
  <div class="child"></div>

</div>