Have you ever tried setting percentage height: 100% in CSS? You must have encountered that this doesn’t work as expected. This is a common issue faced by developers because percentage height in CSS depends on the element’s parent height, which has a defined height. In this article, we will discuss why percentage height is not working in CSS and how to fix percentage height issues in HTML and CSS using CSS Flexbox, Grid, and viewport height (vh) units.
Table of Contents:
How CSS Calculates Percentage Heights
It is important to know how CSS handles height values before fixing the issue. Let’s say that when you set the element height as a percentage, the browser makes this out based on the height of its parent element. If the parent element does not have a set height, the height based on percentage won’t work.
Parent Dependency Issue
While percentage width works based on the viewport or parent block, percentage height in CSS needs the parent height in CSS to be a defined height, which means setting the CSS height as 100% will only work if all the element’s parents’ height in CSS have been defined. If the element’s parent height in CSS isn’t set, the browser can’t calculate the element’s parent height in CSS.
Example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Percentage Height Issue</title>
<style>
.container {
width: 100%;
height: auto;
background-color: lightgray;
}
.child {
width: 50%;
height: 100%;
background-color: lightblue;
font-size: 20px;
}
</style>
</head>
<body>
<div class="container">
<div class="child">Child Element</div>
</div>
</body>
</html>
Output:
In this example, .child is set to height: 100%, but because .container has no height, the child element does not get the expected height.
Methods to Fix Percentage Height
You can define a fixed height by using vh units, flex, and grid layout for this purpose. Let us discuss these methods below:
Method 1: Set Fixed Height on the Parent
You can set the element’s parent height in CSS to make the percentage height in CSS work. If you want the child element to have a CSS height of 100%, make sure the CSS parent height is fixed.
Example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Min-Height Example</title>
<style>
.container {
width: 100%;
height: 500px; /* Fixed height instead of min-height */
background-color: lightgray;
}
.child {
width: 50%;
height: 100%; /* Matches exactly */
background-color: lightblue;
font-size: 20px;
}
</style>
</head>
<body>
<div class="container">
<div class="child">Child Element</div>
</div>
</body>
</html>
Output:
Explanation: You can use this code to create a child element that is half the container’s width and as tall as the container.
Method 2: Use Viewport Height (vh) Instead
You can use this method to make an element’s height in CSS dependent on the viewport instead of its parent height in CSS.
Example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Viewport Height Example</title>
<style>
.full-screen {
height: 100vh;
background-color: lightblue;
font-size: 20px;
}
</style>
</head>
<body>
<div class="full-screen">This div is full height of the viewport.</div>
</body>
</html>
Output:
Explanation: This code makes the div element take the full height using the 100vh.
Method 3: Use Flexbox for Full-Height Layouts
You can use Flexbox to make child elements stretch and fill the available space within a parent container, even when you’re working with percentage height in CSS.
Example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Flexbox Example</title>
<style>
.container {
display: flex;
flex-direction: column;
height: 100vh;
background-color: lightgray;
}
.child {
flex: 1;
background-color: lightblue;
font-size: 20px;
}
</style>
</head>
<body>
<div class="container">
<div class="child">Flex Child</div>
</div>
</body>
</html>
Output:
Explanation: The container is created with the flexbox layout to fill the full viewport height. You can see the child element takes all the available space.
Method 4: Use CSS Grid for Height Control
You can use CSS Grid to make sure that a child element fills the full height of its parent container, even when using percentage height in CSS.
Example:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>CSS Grid Example</title>
<style>
.container {
display: grid;
grid-template-rows: 1fr;
height: 100vh;
background-color: lightgray;
}
.child {
background-color: blue;
font-size: 20px;
}
</style>
</head>
<body>
<div class="container">
<div class="child">Grid Child</div>
</div>
</body>
</html>
Output:
Explanation: This makes sure the layout is flexible for controlling the child’s height because the container is created by the CSS grid to take the full height of the viewport.
Conclusion
Percentage height in CSS often fails because it depends on the parent height in CSS that has been defined. If you are using CSS height as 100% and it is not working, then try defining a fixed height on the parent or use alternatives like Flexbox, Grid, or viewport units. These methods effectively solve the common issues with percentage height in CSS. Thus, after learning methods to how to fix percentage height issues in HTML and CSS, you can easily fix percentage height issues.
Why does percentage height not work in HTML/CSS? – FAQs
Q1. Why percentage height is not working in CSS?
The percentage height in CSS is not working because the CSS parent height might not have a fixed.
Q2. What happens if the parent height in CSS is not defined?
In this case, the child element’s percentage height in CSS is turned to auto, where it takes the content height.
Q3. Can I use percentage height in CSS with min-height or max-height?
No, percentage height in CSS only works with height. Using min-height or max-height alone won’t have any reference height.
Q4. How can I make percentage height CSS work for nested elements?
Make sure every element’s CSS parent height has a defined height.
Q5. Does percentage height in CSS depend on other CSS properties?
Yes, properties like position can influence how CSS height is calculated.
Q6. How to fix percentage height issues in HTML and CSS?
To fix percentage height issues in HTML and CSS, you must have to define the parent height as fixed in CSS or use alternatives like viewport height (vh), Flexbox, or Grid.