Ensure that the child element completely fills the parent element while maintaining a padding around the edges

Question

Ensure that the child element completely fills the parent element while maintaining a padding around the edges

How can I create a child div that fills 100% of the parent's width and height, including padding? I've tried using box-sizing = border-box, but it isn't working. I also attempted adding the box-sizing property to all elements with *, but that didn't change anything either. Here is my code snippet:

html {
  font-size: 16px;
}

.parent {
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  background-color: #ccc;
  width: 100%;
  height: 100%;
  
/* 
--= 100% should include padding =--
box-sizing: border-box; <-- this didn't change anything...
*/
}

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

html css

Answer 1

Answer №1

If a child element is positioned absolutely in relation to its parent, it will be placed outside the parent's padding. To achieve this, use position:absolute as follows:

.parent {
  position: relative;
  padding: 2em;
}

.child {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

Visual Example:

html {
  font-size: 12px;
}
body {
  margin: 1em;
}

.parent {
  position: relative;
  font-size: 1.2em;
  width: 10em;
  padding: 2em;
  margin:1em 0 0;
  background-color: blue;
  border: 5px solid red;
}

.child {
  position: relative;
  background-color: lightgreen;
}

.background {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

p {
  margin: 0;
}
.red {
  color: red;
}
.blue {
  color: blue;
}
.green {
  color: green;
}

<p>Parent Border: <span class="red">Red</span></p>
<p>Parent Background: <span class="blue">Blue</span> (not visible)</p>
<p>Child Background: <span class="green">Green</span></p>

<div class="parent">
  <div class="child background"></div>
  <div class="child">This text to indicate parent's padding</div>
</div>

Implementation with your code:

html {
  font-size: 16px;
}

.parent {
  position: relative; /* ADDED */
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  position: absolute; /* ADDED */
  left: 0; /* ADDED */
  top :0; /* ADDED */
  background-color: #ccc;
  width: 100%;
  height: 100%;
}

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

An Overview:

In the absolute positioning scenario, a box is exactly offset with regard to its container block.

Absolute positioning @ w3

When the position property is set to static or relative, the container block is established by the edge of the content box of the closest ancestral element that functions as a block container...

When the position property is set to absolute, the container block is defined by the edge of the padding box of the nearest ancestral element that has a position value other than static (fixed, absolute, relative, or sticky).

Identifying the containing block @ moz

Emphasis and bold added for emphasis.

For more information: box model

Answer 2

If a child element is positioned absolutely in relation to its parent, it will be placed outside the parent's padding. To achieve this, use position:absolute as follows:

.parent {
  position: relative;
  padding: 2em;
}

.child {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

Visual Example:

html {
  font-size: 12px;
}
body {
  margin: 1em;
}

.parent {
  position: relative;
  font-size: 1.2em;
  width: 10em;
  padding: 2em;
  margin:1em 0 0;
  background-color: blue;
  border: 5px solid red;
}

.child {
  position: relative;
  background-color: lightgreen;
}

.background {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
}

p {
  margin: 0;
}
.red {
  color: red;
}
.blue {
  color: blue;
}
.green {
  color: green;
}

<p>Parent Border: <span class="red">Red</span></p>
<p>Parent Background: <span class="blue">Blue</span> (not visible)</p>
<p>Child Background: <span class="green">Green</span></p>

<div class="parent">
  <div class="child background"></div>
  <div class="child">This text to indicate parent's padding</div>
</div>

Implementation with your code:

html {
  font-size: 16px;
}

.parent {
  position: relative; /* ADDED */
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  position: absolute; /* ADDED */
  left: 0; /* ADDED */
  top :0; /* ADDED */
  background-color: #ccc;
  width: 100%;
  height: 100%;
}

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

An Overview:

In the absolute positioning scenario, a box is exactly offset with regard to its container block.

Absolute positioning @ w3

When the position property is set to static or relative, the container block is established by the edge of the content box of the closest ancestral element that functions as a block container...

When the position property is set to absolute, the container block is defined by the edge of the padding box of the nearest ancestral element that has a position value other than static (fixed, absolute, relative, or sticky).

Identifying the containing block @ moz

Emphasis and bold added for emphasis.

For more information: box model

Answer 3

Answer №2

To achieve this without altering the parent element, you can override the parent element's padding. Start by setting the width and height to calc(100% + 10em). Additionally, adjust the left and top padding values to position the element correctly. Ensure that the child element has position: relative, and set left and top to -5em.

html {
  font-size: 16px;
}

.parent {
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  background-color: #ccc;
  width: calc(100% + 10em);
  height: calc(100% + 10em);
  position: relative;
  left: -5em;
  top: -5em;
}

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

Answer 4

To achieve this without altering the parent element, you can override the parent element's padding. Start by setting the width and height to calc(100% + 10em). Additionally, adjust the left and top padding values to position the element correctly. Ensure that the child element has position: relative, and set left and top to -5em.

html {
  font-size: 16px;
}

.parent {
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  background-color: #ccc;
  width: calc(100% + 10em);
  height: calc(100% + 10em);
  position: relative;
  left: -5em;
  top: -5em;
}

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

Answer 5

Answer №3

To reposition the child element, your child should set its margin to the negative value of the parent's padding. This will return the component to its original position before the padding was added to the parent. Remember, this adjustment can be made in any direction.

Due to the additional padding applied to the parent, the parent's dimensions have increased. Horizontally, this increase is from the sum of left and right paddings. Vertically, it results from the combination of top and bottom paddings.

html {
  font-size: 16px;
}

.parent {
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  background-color: #ccc;
  width: calc(100% + 5em + 5em); /* parent's width + left-padding + right-padding */
  height: calc(100% + 5em + 5em); /* parent's height + top-padding + bottom-padding */
  margin: calc(5em * -1); /* The negative of parent's padding */
}

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

For your specific scenario, a more straightforward approach for the child component would be:

.child {
  background-color: #ccc;
  width: 200%;
  height: 200%;
  margin: -5em;
}

Answer 6

To reposition the child element, your child should set its margin to the negative value of the parent's padding. This will return the component to its original position before the padding was added to the parent. Remember, this adjustment can be made in any direction.

Due to the additional padding applied to the parent, the parent's dimensions have increased. Horizontally, this increase is from the sum of left and right paddings. Vertically, it results from the combination of top and bottom paddings.

html {
  font-size: 16px;
}

.parent {
  font-size: 1rem;
  width: 10em;
  height: 10em;
  padding: 5em;
  background-color: #f0f0f0;
}

.child {
  background-color: #ccc;
  width: calc(100% + 5em + 5em); /* parent's width + left-padding + right-padding */
  height: calc(100% + 5em + 5em); /* parent's height + top-padding + bottom-padding */
  margin: calc(5em * -1); /* The negative of parent's padding */
}

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

For your specific scenario, a more straightforward approach for the child component would be:

.child {
  background-color: #ccc;
  width: 200%;
  height: 200%;
  margin: -5em;
}

Ensure that the child element completely fills the parent element while maintaining a padding around the edges

Answer №1

Answer №2

Answer №3

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