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Introduction #

This handbook and its accompanying code is a reference guide on how to understand and use CSS to build web applications that incorporate responsive design using Grid, Flexbox, and media queries.

You can jump directly to any topic in the table of contents that you are curious about in this handbook, you don’t have to read it from start to finish.

⚡ The source code for this handbook can be found in this github repo.

Great CSS references #

The following references are really useful when working w/ CSS.

Use CSS Reset #

Browsers have defaults (the user agent stylesheet) and you can reset them using CSS Reset. Here’s how you can use it in your React app.

  1. Copy the contents of this CSS file into a file named reset.css. Feel free to modify this file to suit your needs.
  2. Then add @import "reset.css"; to your app’s main CSS file.
  3. You can also add entries for elements like button and input which are not explicitly set by the default Reset CSS stylesheet (and thus end up using user agent stylesheet, which is the default behavior that we don’t want and why we are using Reset CSS in the first place).

Use normalize.css #

Instead of CSS Reset you can also use Normalize.css. Here’s the github repo for Normalize.css. You can either:

  1. Download the CSS file and import it.
  2. Import the CDN URLs (from the repo’s README) which can be found here. Using the unpkg CDN as an example,
  • Here’s the link to v8.0.1: https://unpkg.com/normalize.css@8.0.1/normalize.css
  • Removing the @8.0.1 ends up in the latest version of this file, so I am using https://unpkg.com/normalize.css/normalize.css
  1. Or just get the latest version from the github repo itself: https://necolas.github.io/normalize.css/latest/normalize.css.

Code example

Difference between body and html (:root) #

In CSS html and :root are the same. But, there are subtle differences between them and body. One manifests when we try to use line-height in :root / html. It simply does not work. But it does work when applied to body. Here’s some vague indication as to why this might be happening.

So the following doesn’t work.

:root {
  line-height: 1.5;

html {
  line-height: 1.5;

And the following does.

body {
  line-height: 1.5;

Code example

Local vs global scope CSS variables (custom properties) #

CSS variables are actually called custom properties. Usually they are defined globally in :root. However, it possible to define them locally. I don’t know if this is necessarily a good idea though. Here’s an example.

/* Use local variable, instead of declaring in :root. */
a {
  --my-link-color: lightgray;
  color: var(--my-link-color);

yy a:link {
  --my-link-color: teal;

a:hover {
  --my-link-color: aquamarine;

Please refer to the responsive design section to read about best practices for using variables and CSS (flexbox, grid, etc).

Code example

Using CSS class pseudo selectors to style child elements of a parent #

Using CSS class pseudo selectors in order to style child elements of a parent (which has this style applied) w/out having to manually assign classes to each of these children. Let’s say that the parent element has a class DottedBox, which will do this, here’s the CSS. Here’s a video by Kevin Powell where he uses this pattern for flexbox.

  1. .DottedBox { padding: 8pt; border: 4pt dotted cornflowerblue; }
  2. .DottedBox > * { /* this gets applied to all the children */ }

CSS background-image vs img tag #

Here’s a great SO thread on when to use CSS background-image vs using the img tag. To summarize:

  • Use img tag when the image is part of the content (foreground).
  • Use CSS background-image when:
    1. The image simply goes in the background of the content.
    2. The image should not be printed, if printing the “page” is a use case that needs to be considered.
    3. You need to overlay multiple images, gradients, other images, and apply transparency in layers to the background image, using background shorthand (here’s an example index.css).

Code example

SVG and CSS #

It is possible to style SVG w/ CSS, just as you would HTML w/ CSS. However, there are some browser support issues. Not all the ways are supported by Chrome. There are various ways of importing the CSS file into the SVG file which is where the browser support issues show up.

So the most reliable way might be to use embedded SVG and then style it inline. Or use JS to set the style of SVG elements in the DOM.

CSS layouts #

Box model and CSS sizing #

There are 2 box sizing models. The box-sizing rule determines whether padding and margin are included when calculating the width and height of a “box” / element.

  1. By default it is set to box-sizing: content-box; which does not account for padding and margin.
  2. You can set it to box-sizing: border-box; which “includes” the padding and margins.

Hiding things #

There are two approaches, here are more details.

  1. display:none - This simply removes the element from the page, you can only access it via the DOM.
  2. visibility:hidden - The element is rendered and space is allocated on the page, but it is not shown.

Flow layout - display: inline, block, inline-block #

The display rule determines whether an element is displayed in line or with a line break in a CSS flow layout. By default some elements are displayed inline (such as button). To change this you can specify.

  1. display: block; - box takes up entire width of content whether it fills it or not, and adds line break. Eg: h1, div, p.
  2. display: inline; - box takes up min amount of width for content and does not add a line break. Eg: img, strong, em.
  3. display: inline-block; - mash up of the two above, can set the width and height of each element, and they can be positioned next to each other.

    ⚠ Instead of using this, try Grid and Flexbox which are much better!

The display rule can also be used to switch to flex and grid layouts, which also affect the positioning and sizing of their children elements.

CSS Positioning #

💡 Use Grid and Flexbox instead of absolute positioning whenever possible.

Absolute and relative positioning #

References and notes

  • MDN docs on position
  • The top, right, bottom, and left properties determine the final location of positioned elements.
  • position: absolute takes the element out of the flow of the normal page and puts it in its own layer. This can be useful for popups and other UI that needs to be in a fixed position on the page.
    • This element should be placed in a parent which is also positioned, usually using position: relative.
    • Normal elements are positioned relative to the viewport.
  • You can also use the z-index property in order to how the element “stacks up” when changing the default positioning of elements.

Fixed positioning #

  • This works in exactly the same way as absolute positioning, with one key difference:
    • whereas absolute positioning fixes an element in place relative to its nearest positioned ancestor (the initial containing block if there isn’t one),
    • fixed positioning usually fixes an element in place relative to the visible portion of the viewport.

Sticky positioning #

  • This is a hybrid between fixed and relative. It allows a positioned element to act like it’s relatively positioned until it’s scrolled to a certain threshold (e.g., 10px from the top of the viewport), after which it becomes fixed. This can be used, for example, to cause a navigation bar to scroll with the page until a certain point and then stick to the top of the page.

CSS floats #

⚠ Use Grid and Flexbox instead of this.

Flex layout - display: flex #

Code example

References and notes

  • flex-direction: row or column.
  • The most important thing to note about Flexbox is that in order for Flexbox layout to be activated in a hierarchy of DOM nodes, at least one parent must have display: flex declared. This is called the flex container.
  • A DOM element can have Flexbox directives that apply to itself and others that apply only to its immediate children. This is called a flex item. Since a DOM element can be a child of another Flexbox parent, and itself be a parent for other Flexbox nodes.

Here’s the Flexbox parent style called flexCardsContainer. This contains flex items which are the cards themselves. Each card itself is a flex parent which contains flex items.

.flexCardsContainer {
  --alpha: 0.3;

  /* Flexbox - for children (cards). */
  display: flex;
  flex-wrap: nowrap;
  align-items: stretch;

  counter-reset: cardCounter;

  padding: var(--defaultPadding);
  color: yellow;

Here’s .card an example of a CSS class that is both a parent and child.

.card {
  /* Flexbox - for children (card contents). */
  display: flex;
  flex-direction: column;

  width: fit-content;
  margin: var(--defaultPadding);
  padding: var(--defaultPadding);
  background: rgba(0, 0, 0, var(--alpha));
  border-radius: var(--defaultBorderRadius);

  /* Flexbox - for self. */
  align-items: center;
  justify-content: flex-start;

Here are some interesting things to note.

  • align-self overrides default alignment that is set for a flex item on the cross axis.
  • flex-basis is the initial size of a flex item that will be added to if flex-grow is specified.
    • Docs.
    • You can also just use the flex shorthand and supply flex-grow, flex-shrink, and flex-basis values in one go.

Grid layout - display: grid #

Code example

References & notes

Media queries & responsive design #

  • MDN guide
  • Make sure the HTML has a viewport meta tag . that sets it up to work on mobile browsers.
  • CSS variables don’t work here unless you use a CSS preprocessor.
  • Usually the directives are something like, something should be applied if:
    • Greater than a certain width: min-width or min-device-width
      • Eg: if screen is less than 70ch wide => @media screen and (max-width: 70ch)
    • Less than a certain width: max-width or max-width
      • Eg: if screen is greater than 70ch wide => @media screen and (min-width: 70ch)
  • You can match for things like
    • width
    • height
    • device-height
    • device-width
    • orientation
  • For responsive design, the idea is to start w/out any media queries for a mobile first design. Then add min-width (aka greater than this breakpoint) overrides at breakpoints to handle larger screens.
    • You can add a few of these larger and larger breakpoints - perhaps a mobile, mid size, and large layout.
    • Each of these “larger screen overrides” simply describes the differences between it and the previous size, and they’re all based on the mobile first styles.
    • There are no hard and fast rules for these breakpoints. You just have to eyeball it for your app / content and make choices for what these exact breakpoint values should be.
  • You can use CSS variables in your responsive design. Defining and using these variables in styles makes it relatively simple to override them when various breakpoints are hit. Things like changing the number of CSS grid columns, choosing which Flexbox direction to use, and even margin, padding, and block visibility can be done using them. Here’s an example.

    .gridCardsContainer {
      --gridNumCols: 1;
      display: grid;
      grid-template-columns: repeat(var(--gridNumCols), 1fr);
    /* If the screen is < 70ch wide. */
    @media screen and (max-width: 70ch) {
      .gridCardsContainer {
        --gridNumCols: 1;
    /* If the screen is > 70ch wide. */
    @media screen and (min-width: 70ch) {
      .gridCardsContainer {
        --gridNumCols: 2;

Code example

No JS (only CSS)

Keyboard focus and mouse click detection


  • When a modal dialog is shown it takes up the entire viewport. So if you were to call document.elementFromPoint(x,y) with any x and y coordinate in the viewport, the same element would be returned (which is the modal dialog)

    elementFromPoint API docs.

  • In order to close the dialog if a click occurs outside the dialog is very difficult to do, since technically the entire dialog is visible, so all clicks are simply being generated by the dialog. So if a click listener was added to document, then then on every click, the event.target would always be the same modal dialog element.
  • By default, pressing the Esc key will close the dialog.
  • Adding a focusout listener on the modal dialog doesn’t really do much. In the code example used here the focus is actually on the “Ok” button, and as soon as any click or keypress is made the focus is taken away from it, and this button is what event.target references in the listener. It is possible to simply close the dialog when any click or key press occurs, but that seems janky, given Esc is already hooked up by default to do this.

How to add emoji to website in HTML, CSS, or JavaScript #

Let’s say you want to add this emoji 🔥 to your HTML and CSS, with codepoint U+1F525, here are the steps.

💡 Tutorial - How to add Emoji’s in your website, using HTML, CSS or JavaScript

  • CSS

    You must replace the U+ with \0 in the codepoint. So instead of U+XXYYZZ you use \0XXYYZZ

    .card h3:before {
      counter-increment: cardCounter;
      content: "\01F525 \01F5C3 \01F4C7 Card #"counter(cardCounter) " - ";
  • HTML

    You must replace the U+ with &#x. So instead of U+<code> you use &#x<code>.

    <h3>This is a modal dialog &#x1F44B</h3>
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giti in action

edi in action

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