Interesting Facts About CSS Box Model Last Updated : 27 Feb, 2025 Comments Improve Suggest changes Like Article Like Report The CSS Box Model is the foundation of layout and spacing in web design. Let’s explore some interesting facts that will help you work with it more effectively.1. Padding and Border Expand the Element SizeMany developers forget that padding and borders add extra space around an element, which can unexpectedly change the overall size of the element.Element size increases: The width and height of the element are affected by padding and border.Box-sizing matters: The default box-sizing: content-box includes padding and border in the element’s total size. HTML <html> <head> <style> .box { width: 200px; height: 100px; padding: 20px; border: 5px solid black; background-color: lightcoral; } </style> </head> <body> <div class="box"></div> </body> </html> The total size of the .box increases because of padding and borders.The total width becomes 250px (200px + 20px padding + 5px border on each side).The total height becomes 150px (100px + 20px padding + 5px border on each side).2. Box-Sizing Can Control Element Size CalculationThe box-sizing property controls whether padding and border are included in the element’s total width and height, which is useful for consistent layout management.Content-box: Padding and border are added outside the width and height (default).Border-box: Padding and border are included inside the width and height, keeping the size consistent. JavaScript <html> <head> <style> .box-content { box-sizing: content-box; width: 200px; padding: 20px; border: 5px solid black; background-color: lightgreen; } .box-border { box-sizing: border-box; width: 200px; padding: 20px; border: 5px solid black; background-color: lightblue; } </style> </head> <body> <div class="box-content"></div> <div class="box-border"></div> </body> </html> The .box-content uses the default box-sizing: content-box, so padding and border increase the total size.The .box-border uses box-sizing: border-box, so padding and border are inside the 200px width and height.3. Negative Margins Can Pull Elements CloserNegative margins allow elements to overlap or move closer than their normal layout would allow.Overlapping elements: Negative margins pull the element towards neighboring content.Fine-tuning: They are useful when you need precise layout adjustments.Can cause overlap: Negative margins can make elements overlap if used incorrectly. HTML <html> <head> <style> .box { width: 200px; height: 100px; background-color: lightyellow; margin-bottom: -20px; /* Negative margin */ } </style> </head> <body> <div class="box"></div> <div class="box" style="background-color: lightpink;"></div> </body> </html> The first .box has a negative margin, which pulls it closer to the second .box.This causes both boxes to overlap slightly.4. Auto Margin Can Center Flex ItemsUsing margin: auto on flex items is a simple and powerful trick to center them within a flex container.Centered items: margin: auto centers the item horizontally or vertically.No extra properties: No need for additional positioning or calculations.Works with flex containers: This only works inside a flex container. HTML <html> <head> <style> .container { display: flex; height: 100vh; } .box { margin: auto; width: 200px; height: 100px; background-color: lightseagreen; } </style> </head> <body> <div class="container"> <div class="box"></div> </div> </body> </html> The .box has margin: auto, which automatically centers it within the .container.This centers the box both horizontally and vertically. Comment More infoAdvertise with us Next Article CSS Introduction A anujpaz9pe Follow Improve Article Tags : Web Technologies CSS Similar Reads CSS Tutorial CSS stands for Cascading Style Sheets. It is a stylesheet language used to style and enhance website presentation. CSS is one of the three main components of a webpage, along with HTML and JavaScript.HTML adds Structure to a web page.JavaScript adds logic to it and CSS makes it visually appealing or 7 min read CSS Introduction CSS (Cascading Style Sheets) is a language designed to simplify the process of making web pages presentable.It allows you to apply styles to HTML documents by prescribing colors, fonts, spacing, and positioning.The main advantages are the separation of content (in HTML) and styling (in CSS) and the 4 min read CSS Syntax CSS is written as a rule set, which consists of a selector and a declaration block. The basic syntax of CSS is as follows:The selector is a targeted HTML element or elements to which we have to apply styling.The Declaration Block or " { } " is a block in which we write our CSS.HTML<html> <h 2 min read CSS Selectors CSS Selectors are used to target HTML elements on your pages, allowing you to apply styles based on their ID, class, type attributes, and more. There are mainly 5 types of selectors.Basic CSS Selectors: These are used to target elements by tag, .class, or # ID for fundamental styling needs.Combinato 7 min read CSS Comments CSS comments are used to add notes or explanations to your code, helping you and others understand it better. They start with /* and end with */ and can be used for both single-line and multi-line comments. Note: Comments are ignored by browsers, so they won’t affect how your webpage looks or works. 2 min read CSS Colors CSS colors are used to set the color of different parts of a webpage, like text, background, and borders. This helps make the page look more attractive and easier to read. You can define colors using names, hex codes, RGB values, and more.You can try different formats of colors here- #content-iframe 5 min read CSS Borders Borders in CSS are used to create a visible outline around an element. They can be customized in terms ofWidth: The thickness of the border.Style: The appearance of the border (solid, dashed, dotted, etc.).Color: The color of the border.You can try different types of borders here- #custom-iframe{ he 5 min read CSS Margins CSS margins are used to create space around an element, separating it from neighboring elements and the edges of the webpage. They control the layout by adjusting the distance between elements, providing better organization and readability.Syntax:body { margin: value;}HTML<html> <head> 4 min read CSS Height and Width Height and Width in CSS are used to set the height and width of boxes. Their values can be set using length, percentage, or auto.Width and HeightThe width and height properties in CSS are used to define the dimensions of an element. The values can be set in various units, such as pixels (px), centim 4 min read CSS Outline CSS outline is a property used to draw a line around an element's border. It does not affect the layout, unlike borders. It's often used to highlight elements, providing a visual emphasis without altering the dimensions of the element.Syntaxselector{ outline: outline-width outline-type outline-color 4 min read Like