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:

Answer 1

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: #ffffd;
}