HTML and CSS lesson 14: The box model: padding, border and margin

UK version. UK school years and UK spelling. · US version of this lesson

Every element is a box: content, then padding, then border, then margin. Normally width is just the content; box-sizing: border-box makes it the whole box. A complete 40-minute HTML and CSS lesson for beginners (Year 7, KS3), from Unit 5: Boxes and layout. You build real web pages right here in your browser – nothing to install.

Time: 40 minutes + 20 min homework
Year: Year 7, KS3 (ages 11–12)
You need: A computer or tablet, paper and a pencil
Marked: Instantly, with explanations

For parents: how to use this lesson

You don't need to know HTML yourself. The lesson explains each step on screen, the way Mr Babbage, our Head of Computing, likes it: a worked example first, then a go for your child. When your child builds a page, the browser draws it straight away and Classfern marks it with a checklist.

Read what your child will learn together.
Press Start the lesson below. Sit with your child for the teaching and the worked example (about 15 minutes): ask them to point at each tag and say what it does.
Let them do the practice on their own. If a page doesn't look right, the checklist says what is missing – let them find the mistake before you help.
Finish with the exit questions and the talk question: “Why might designers like `box-sizing: border-box`?”
Later that day or the next day: the homework (20 minutes), then a practice test.

Watch out for

width includes padding. Only with box-sizing: border-box.
Margin is part of the box's width. Margin is space outside the border.

Miss Lovelace's tip for home: ask your child to change one thing on their page – a word, a colour, a size – and predict what will happen before they look. Predicting first is how programmers learn fastest.

What your child will learn

We are learning to name the four parts of the box model.

Success looks like

I can name the four parts of the box model.
I can work out how wide a box is on screen.
I can use padding, border, margin and box-sizing.

Key words

box model · content · padding · border · margin · box-sizing · shorthand

What to have ready

A device with a web browser (pages are built and checked right in the browser – nothing to install)
Paper for planning and sketching
A keyboard helps for typing code (a tablet works too)

The big ideas (for the adult)

Every element is a rectangle with four layers, from the inside out: the content, the padding (space inside the border), the border, and the margin (space outside the border, pushing other boxes away).

Normally width sets only the content. Padding and border are ADDED on both sides: width: 200px; padding: 10px; border: 5px solid; is 200 + 20 + 10 = 230px wide on screen. Margin is outside, so it doesn't count. With box-sizing: border-box;, width means the whole box, which is easier to plan.

A border needs a style: border: 3px solid red;. Without solid (or dashed, dotted…) there is no border at all. Shorthands save typing: padding: 10px 20px; is 10px top and bottom, 20px left and right.

Worked example: a 230px box

CSS:

.box { width: 200px; padding: 10px; border: 5px solid navy; margin: 20px; }

HTML:

<div class="box">A box</div>

The lesson, step by step

40 minutes in 5 parts
Part	Time	How it is checked
Starter	5 min	Marked by Classfern
Learn	8 min	Read, watch and talk
See it	7 min	Marked by Classfern
Practise	15 min	Marked by Classfern
Check and reflect	5 min	Marked by Classfern + self-check

The lesson

It runs here on the page. No sign-up and no names – nothing you type is sent anywhere. Each visit picks a new mix of questions.

Homework

20 minutes: predict what the browser will do, build or fix a short page, and check the key ideas – then a short reflection. New questions every time, all marked instantly.

Practice tests

All KS3 computing practice tests · All 20 HTML and CSS lessons

Curriculum

National curriculum in England, computing, key stage 3: pupils should be taught to use 2 or more programming languages, at least one of which is textual, to solve a variety of computational problems; make appropriate use of data structures [for example, lists, tables or arrays]; design and develop modular programs that use procedures or functions; and to design, use and evaluate computational abstractions that model the state and behaviour of real-world problems and physical systems.

Contains public sector information licensed under the Open Government Licence v3.0.

Our lessons and questions are our own. They are not written or endorsed by any government department, testing agency or exam board. HTML and CSS are open web standards; Classfern is not affiliated with the organisations that publish them.