Thank you so much.


It's really nice to be here.

It's like my first time and I'm like enjoying it.

But but not not like for for like, for like thing and like sleeping, but yeah, I'm like Okay.

Almost 2 years ago I published an article called.

Which is like basically was like a listing of like CSS steps and back then I didn't like, thought about this it just was like a listing like of CSS steps, but it's good.

I think it's a good over one 100 K page views in less than two weeks and that thing actually has like got, good me got like got me to think about this into why not like to turn this like into a standalone thing.

I just did that.

So now it's, kind like a well known fact that I, unknown content can like, cause CSS issues okay.

Be it like having a alone content or maybe a short content or having an image with having an list, like an image like with a different aspect ratio.

Here we can see this this kinda like an example where where we have a headline and on the right side we have this view all link.


So when we change the text in here, we need to think about what should happen.

Do we want the headline to to of like run into a new line?

Or do we wanna to have each one of them like in the same like in a new line?

None of them is actually bad, but the idea is that we need to think about that.

We need to decide what should happen when the content become like this.

And for the same component here we have this list of cards and each one has a thumbnail.


And for now it looks good, but when we change the image to something that has a different aspect ratio we will end up with that.

So the image looks like this.

And in this case I would like to ask is the image that that we will use in here will will have always like the same aspect ratio?

And if not what we should, do about it?

Modern CSS made our life really easy.

So now we have things like flexbox and CSS grid and CSS has and the min-max and we have so many things, but with all of that, we still face layout issues.

And that is not because of CSS, of course.

It's because sometimes we write CSS without actually thinking about what should happen when the content changes.

So here we have this this kinda like vertical design.

We have like headline and it takes, and it looks good.

And the person who actually built this design said, 'Hey the design is ready, and it's just looks fine.' Okay.

So when when I tried that and I tried to place some content it looked like this.

When we added like a very long content it seems like the ??? has a fixed height and that has led like the content is kinda like blowing out as you see here.

And the same thing also apply for the image.

The image actually has a fixed height.

So when we replace some when we replace that image we ended up with that issue.

And as you see all of these like issues in here is just because just like I replace the content.

We can take something from this design, which is this one.

So here we have this kind, like guard component.

We have an image we have a name.


In this, like such a like in such a case we can think about all the all those edge cases.

When we have a no title or when we want to.

Let's say like the add to action or something else, or will we have an image with a different aspect ratio.

And that has led to this thing.

It's all about writing CSS and thinking about what should happen if we change the content.

And it's, not only for people who write CSS, but it can be be like very useful in cases like when we design things or when we test things.

So when we design we, can design with unknown content in mind.

So here is the same example, but let me show you this first.

We can we can actually think with what if' content what if, we like, have a like a very long title or what if we replace this let's say this maybe this kind of image with something that has a different aspect ratio.

So it's, like designing with thinking about kinda like all the edge cases we will have.

And when we write CSS, we can think of it as an advanced CSS reset.

We can overflow to like all the h1 and, the h2.

And like these things or maybe we can add object fits to like, to all the images we have.

And when we test things it can be really helpful to have this this kind of listed like a common list of CSS issues that we should test for.

And for me, I like to think of these CSS features as as a way that can that can that can actually help us in fixing issues.

So we have things like the min the min-height the min-width the flex-wrap and also sorts of these things.


Now let's get into some CSS tips.

The first set is all about images.

So as the first one is about having like max-width.

On the left we have the same image, and on the right we have like the same example, but without max-width.

We need to make sure to to include max-width so we can have all the images like within like, within their space they have.

Next is having let's see, like a background image.

In in this example we have an image and on the right we have the same one.

But when we resize the screen that's that kind of image will actually repeat on the x-axis.

What what we can do is to simply just add background-repeat: no-repeat.

And this will fix the issue.

Here we can see that in action.

So when I resize and and have no-repeat the image will just stay within this block or this parent.

And when we have repeats it'll look like this.


Next is about image dis distortion.

Here we have this card component.

For now it looks good, but when I change the image to something different, to something with a different aspect ratio it'll look like that.

In in this case I would simply add object-fit and make and make make the image like feel the whole space.

And here again, we can see that in action.

So when I resize, I notice how the image is getting distorted.

And when I turn the object-fit fit, it'll actually fill fill the space it has.


Next is having a text over an image.

In, in this example we have a text over an image, and for now it looks fine, but when that image fails to load we will end up with that.

If we are using an H…, if if if like we let's see, like we are using an HTML image tag we can add a background color and it'll work like in the case when the image fails to load.

So that can help sometimes.


The next set of tips is about flexbox.

So the first one is about flex-wrap.

In this this example, we have this list.


We have the we have display flex.

Okay, so when when like I resize we will go this this kind of scroll bar.

And the effects in such a case can be simple, which is to add flexwrap: wrap and that will fix the issue.

And here we can see that in action.

So when I turn the lex-wrap on they will just flow into a new line without being like, bad looking.


Next is it's, like a default thing.

In flex box.

So here we have this HTML.

We have an image and then we have a div that contains an h2 and a h3, and a p element.


When we have flex box in here, and when we add a very long like text element that's that's this image will will kinda like stretch to fill the space and we can fix that by simply adding align-self to the image, and it will just like align let's like on the start of this parent element Okay.

Here we can see that in action.

So when I resize, okay, notice how the images is getting the full height, and when I turn align-self on, it'll just stay at the top.


And next is the flex min content size.

This is this is like a very lucky, tricky thing.

So here we have we have an element let's say that on the left you have an image and then we have a name.

So when this name let's say I got like a very long word.

It'll blow out like this.

And the first thing we must think of is that okay, we can use this is overflow-wrap and it'll just fix it.

But no this won't actually fix that.

What we can do is to reset the min-width because let's, is like a flex item will that kind of like the min width for it will be equal to the content.

We need to reset that.

And here we can see that in action too.

So when I resize notice how the content is, It's like blowing out and now when I reset the min-width, it's all good.


And next is avoiding the space between.

When we use that for spacing it can look good when when we have a fixed number of items.

But when we let's say that that we have three items this this kind of list will look like that.

So it's not good.

And like instead of that we can simply use gap or maybe margin and things like that.

And here's the video.

So when I resize, notice how the spacing is kinda like messy, but when I change it to gap and resize, it just looks normal.


The next set is is like all about CSS grid.

So the first one is the min-content size.


So here we have this main section and then we have an aside.


When the main section there is there is kind like a scrolling like element in here.


But when we have that, it will it'll like, cause like that section to actually blow out.

And the reason here is like the same with the min-content with flexbox because the min-content of this section will be equal to the to how let's say to how much items it's it has in here.

So the text again, can be maybe we can replace the one of our with min-max, or maybe you can add maybe like we can add min-width we have so many fix its for that.

But the one I will go for is the min-width.

So here we can see that too.

Notice that when I reset the min-width the section will scroll normally, but without min-width, it it'll just blow out.


Next is about the auto-fit and and auto-fill.

And I think that each time I use them I like, need to look into that figure because the fun fact is that when we use auto-fill it's won't fill this space it has, but from its name, it says that, okay, it's it like we'll fill the space.

But when we use auto-fit it'll actually fill the space.

So it's a little bit odd for me.


Here we have this kind of a grid, okay?

And we have we have like auto-fit.


So when we have four when when we have four items it'll look good.

But when we have only one item, it'll fill the whole space.

And that is not good, of course.

And we can simply replace it with auto-fill so it won't fill the space.

And here, we can see that.

When we have only one item and we are using min-max, it's won't fill that space.

And here we can see that in action too.

So when I resize, notice that now we have like two empty spaces because I because I'm using the auto-fit in here.


So next is about CSS grid fixed values.

So when, we use let's say like a fixed with for a column, and when we resize the screen like this we will have an issue.

The fix will be really simple which is just to use like, Hey I want to apply, like this grid.

We need when we have that kind of space @media min-width blah, blah, blah.


And the next next few things is is like about content.

The first one is about long content.

Here we have this card component where we have a name, and next to that name there's an action.

When we have a very long name it can cause that action like to move into the next line.

The fix here can can be simply to use a flex: 1.

. And we will also need to reset the min-width just in case we have very long content.

Or maybe you can we like trucate and add those dots at the end as you see here.

But I, might not do that in and like all the cases because maybe the content is like important and we don't want this thing.


We can see that in action too.

So notice that when I like turn it off it'll truncate and….


The next step is about having a space between the items.

So here we have this headline, and on the right we have an icon.


When we have very long content in here that icon will end up like colliding with the text.

And in this case the effects can be reasonable which is just maybe we can add margin or gap or a padding or anything else.


And here we can see that.

This this, kind of block in here is is actually the, the spacing.

So when I resize it'll it'll have a safe space between the headline and the link.

Okay, next is about fixed sizes.

So here we have this this hero section with this fixed, height.

And when we have a very long content it'll cause that text to blow out and the fix can be re can be very simple, which is just to show min-heights like instead of using, height.

And the same thing can also apply to width.

So when we have a fixed-idth for an element that contains text it can get like really bad when we replace the text with something like this.

So yes, we need to replace that with min-width too.

And here we can see this example in action.

So when I replace the min-height replace the height with a min-height it'll look good.


Next is is about like scroll bars.


Here on the left we have a box.

And we have some content and when the content is long we have a scroll bar, but on the left sides the content is short, but we still have a scroll bar because we are using overflow-y scroll.

And this will show the scrollbar at at all cases.

And what we can do instead is to replace that with overflow auto . So now when we replace that thing the scrollbar will show only when we have long content.


And next is about the scrollbar the scrollbar gutter.

On the left we have a block with text.


It looks fine, but when when the content become like really big that content will shift because it's it's need, to reserve this is space for a scroll bar.

And so the content will shift.

So what we can do now is we can reserve this space and when the content actually grows it won't cause a Layout shift.

I can show you that in a, in action here.

So I notice that when I add the content it's, kinda shifted to the left.

But when, I reserve the space and then add the content it'll just it'll just be fine.

And we we won't have any shifts.


Next is about the scroll chaining.

In this example when we scroll all the way down and keep scrolling the body element will actually scroll too.

So now we can fix that by resetting the by, resetting the the overscroll behavior.

And what will that do?

Is that it'll contain the scrolling within that space.

As you see in this in this blue outline.

And here, notice that when I when I scroll down and keep scrolling, the body will will scroll.

But when I reset the overflow overflow-scroll and keep scrolling it'll just stay within that box.

And that was was like the whole thing.

Please try to write CSS in a way that can help, like to prevent issues.

And because that can actually it can save so much time and like instead going, Hey, I want to test this whole thing.

No we can rightly assess from the start that can actually account for like, all type of content.

And that was all.

Thank you so much.

A bit of history

Screenshot of article 'Defensive CSS'

Unknown content can break layouts

Illustration of a card with a header, and a list of three components. Each component has an image to the left and text to the right.

Three versions of the card. Original, Title is wrapped into a new line, Pushed the link to a new line

Original card illustration, now the images are thumbnails, not stylised.

Card as above, with a focus on the second item in the list. Arrow points from the image to the text "An image with a different aspect ratio". The image appears 'squashed'.

Is the image coming from the backend always have a consistent aspect ratio?

Modern CSS made our life easier

with all that, we still face layout issues

Not because of CSS, of course...

Perfect Design

Screenshot of a page for a bakery. There are a top level menu, a hero header, and a series of horizontal lists of card containing an image and short text.

Same page, with long vertical text in the header hero, that flows into the main part of the page.

Example Component

An illustration of a component. It's a rounded rectangle. At the top is an image of muffins. Below is the text "muffins" and an add to shopping cart icon aligned vertically.

4 versions of the component. The key take aways are

object-fit: cover–Avoid the image being stretched

Padding from the right, or gap, are important

Defensive CSS

Strategy to write bulletproof CSS


Designing component with unknown content in mind

Frontend Developers

It can act as an advanced CSS reset

QA Engineers

Can be a checklist of common UI issues to test

What if..?

CSS trouble maker

Repeat of the slide with 4 components and takeaway lessons.

Frontend Developers

Think of it as a CSS Reset

/* [1]] Break words when there is enough space */
h1, h2, h3, h4, h5, h6, p, a {
	overflow-wrap: break-word; /* [1] */

[1] Set a maximum width for an image
[2] Let the image cover its bounding box to avoid distortion.

img {
	max-width: 100%; /* [1] */
	object-fit: cover; /* [2] */

QA Engineers

Checklist to common UI issues to test

Defensive CSS Properties

  • flex-wrap
  • object-fit
  • overflow-break
  • padding
  • min-width
  • min-height
  • max-width
  • max-height
  • overscroll-behaviour
  • scrollbar-gutter
  • overflow
  • Background colors
  • Media queries
  • Border

Defensive Tips


Defensive Tips

Image maximum width

Illustration of a rectangular component with an image and padding around it. Beneath is a horizontal line with arrows at each end the width of the image.

Defensive tips / Image maximum width

Illustrations of two components that Ahmad describes.

Defensive tips / Image maximum width

img {
	max-width: 100%;
	object-fit: cover;

Defensive Tips

Background repeat

Illustration of a component with a repeating background image.

Two versions of an element containing the same image. The left is labelled 'small screen', the right 'large screen'. The image is repeated on the right and cut off mid way.

hero {
	background-image: url('..');
	background-repeat: no-repeat;

Screencast of this in action. Ahmad describes the effect.

Defensive Tips

Image Distortion

A rectangular component wth an image above and text below.

Shows an image squeezed horizontally in the component

The component with the image not squeezed as before.

card__thumb {
	object-fit: cover;

Screencast of the technique in action–Ahmad describes the effect.

Defensive Tips

Text over image

A rectangular component with text centered vertically and horizontally over an image

Same component with background mage missing and the text barely visible.

Shows element with image loaded and not loaded. Text is now visible on a contrasting background.

card__img {
	background-color: #2a3137;

CSS Flexbox

Defensive Tips

Flexbox Wrapping
.options-list {
	display: flex;

A rectangular component containing a horizontal list of of transport icons.

.options-list {
	display: flex;

The same component, now narrow, with the list overflowing horizontally, and a scrollbar appearing

.options-list {
	display: flex;
	flex-wrap: wrap;

The same narrow component, with the icons on two lined within the component.

Screencast of the technique in action–Ahamad describes the effect.

Defensive Tips

Default flexbox stretching
<div class="person">
	<img class = "person_ _avatar" src="img/avatar. ¡pa" alt=">"
	<div class="person__content">
		<h3>Ahmad Shadeed</h3>
		<p><! -- Description goes here.. --></p>

.person {
	display: flex;

Same component repeated twice vertically. Each contains an image on the left and heading and text on the right. The component labelle default has a round image. The one labelled 'long content' has the image stretched vertically.

.person avatar {
	/* other styles */
	align-self: start;

Same two components as just before, now the 'long content' component has the image as a circle.

Screencast of this technique in action. Ahmad describes the effect.

Defensive Tips

Flexbox Minimum Content Size
.card {
	display: flex;

Two rectangular components, containing an image then text vertically aligned. The first the text is entirely contained within the component. The second has a long final word that overflows the component horizontally.

card__title {
	overflow-wrap: break-word;

won't have an effect

Identical two components

card title {
	overflow-wrap: break-word;
	min-width: 0;

The second card is shown now breaking inside the long word and making the component taller.

Screencast of this technique in action. Ahmad describes the effect.

Defensive Tips

Avoiding space-between
justify-content: space-between

4 identically sized rounded rectangles aligned vertically.

justify-content: space-between

3 identically sized, evenly spaced rounded rectangles aligned vertically.

wrapper {
	display: flex;
	flex-wrap: wrap;
	gap: 1rem;

3 identically sized, evenly spaced rounded rectangles aligned vertically. The are horixonttally aligned to the left with a gap inside their parent to the right.

Screencast of this technique in action. Ahmad describes the effect.

CSS Grid

Defensive Tips

CSS Grid Minimum Content Size
<div class="wrapper">
	<section class="section"></section>
@media (min-width: 1020px) {
	wrapper {
		display: grid;
		grid-template-columns: 1fr 248px;
		grid-gap: 40px;
.section {
	display: flex;
	overflow-x: auto;

Illustration of a page layout. At the bottom is a horizontal list of rectangular components, with the right most cut off. A label points to this and says 'This is a scrolling container'.

.section {
	display: flex;
	overflow-x: auto:

Stylised view of this layout in dev tools. Ahmad describes what we see.

On the parent level:

  • Replace 1fr with minmax(0, 1fr)

On the grid item level:

  • Set min-width: O on the grid item
  • Set overflow: hidden

Stylised view of this layout. Ahmad describes what we see.

Screencast of this technique in action. Ahmad describes the effect.

Defensive Tips

Auto-fit Vs Auto-fill
repeat (auto-fill, minmax(200px, 1fr));

Don't auto expand the cols when more space is available

Shows four evenly spaced solid rectangles of equal size and a dotted rectangle to the right aligned vertically.

repeat(auto-fit, minmax (200px, 1fr));

Expand the cols when more space is available

Shows 4 evenly spaced,vertically aligned solid rectangles stretched to fill the container.

wrapper {
	display: grid;
	grid-template-columns: repeat(auto-fit, minmax (250px, 1fr));
	grid-gap: 1rem

Horizontal list of 4 components of equal size, distributed horizontally evenly. Below is a single component that fills the same space as the four above.

wrapper {
	display: grid;
	grid-template-columns: repeat (auto-fill, minmax(250px, 1fr));
	grid-gap: 1rem;

Same four components evenly spaced as previously. The component below is now only as wide as the 4 av

Screencast of this technique in action. Ahmad describes the effect.

Defensive Tips

CSS grid fixed values
wrapper {
	display: grid;
	grid-template-columns: 200px 1fr;
	gap: 1 rem;

Illustration of a two component grid layout. The leftmost is labelled 200px, the right 1fr and is wider.

Be careful of fixed values in CSS grid. They will break on mobile

The same layout as above in a narrow screen. The right hand component now overflows horizontally.

wrapper {
	display: grid;
	grid-template-columns: 1fr;
	gap: 1rem;
@media (min-width: 600px) {
	wrapper {
	grid-template-columns: 250px 1fr;

The layout from before now flows vertically with the components flowing down the page.

Defensive Tips

Long Content

Two card components side by side. On the left labelled 'default' and right 'long content'. Each have an image with text below. On the left there's short text and a heart icon aligned vertically to its right. On the right the text wraps and the icon is pushed below the text.

title {
	white-space: nowap;
	overflow: hidden;
	text-overflow: ellipsis;

Component that was on the right, but long text is now truncated on a single line and icon is to its right.

Screencast of this technique in action. Ahmad describes the effect.

Defensive Tips

Component Spacing

A rectangular component with a heading and text below. There's a settings icon in the top right corner.

The same component with longer heading text that runs under the settings icon

.section title {
	margin-right: 1rem;

Both components showing. A right margin is indicated for each heading. With the longer heading it stops the text run under the icon.

Screencast of this technique in action. Ahmad describes the effect.

Defensive Tips

Fixed sizes
hero {
	height: 350px;

Long content causes a her component to overflow its height.

button {
	width: 6rem;

Long text overflows its fixed width button.

.button {
	min-width: 6rem;
	padding-inline: 1rem;

Button now expands to the width of its text.

Screencast of this technique in action. Ahmad describes the effect.


Defensive Tips

Scrollbars on demand
overflow-y: scroll

Two components. Both with visible scrollbars.

Content is long The scrollbar is visible

Content is short The scrollbar is visible

element { overflow-y: auto; }
overflow-y: auto

Same two components Thew one with long content has a scrollbar, the other doesn't.

  • Content is long The scrollbar is visible
  • Content is short The scrollbar is not visible

Defensive Tips

Scrollbar gutter

Two components with padding around them. On the right a scrollbar is shown because the content is longer.

.element {
	scrollbar-gutter: stable;
	overflow-y: auto;

The same components, with additional spacing to the right. On the left this is labelled 'Scrollbar space is reserved'. On the right 'Content grows. No layout changes'

Screencast of this technique in action. Ahmad describes the effect.

overscroll-behavior: auto

When we reach the modal boundary, the scrolling will start on the body content

A dialog open n top of a page. Each is scrolled to the bottom. Arrow points to the page and says "Body scrolls after modal content ends"

modal__body {
	overscroll-behavior-y: contain;
	overflow-y: auto;
overscroll-behavior: contain

The scrolling is contained within the modal

The modal from before is outlined in blue.

Screencast of this technique in action. Ahmad describes the effect.

Give Defensive CSS a try

Thank you