CSS

CSS Pro Tips

A collection of practical tips for writing CSS that is fast, clean, and bug-free — with Bad ↔ Good comparisons.

💡How to read: each tip has a Bad pattern (the old way) ↔ Good (the modern way). Once learned, you can apply it right away.

0. A solid reset from the start

Eliminate inconsistencies between browsers, laying the foundation for every tip below.

css
*, *::before, *::after { box-sizing: border-box; }
* { margin: 0; }
body { line-height: 1.5; -webkit-font-smoothing: antialiased; }
img, picture, video, canvas, svg { display: block; max-width: 100%; }
input, button, textarea, select { font: inherit; }

💡Understand the box model first → when learning Tailwind, utilities like p-*, m-*, border-* will feel very natural.

1. Center — Flexbox > absolute hack

Bad

css
.classic {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

Good

css
.classic {
  display: flex;
  justify-content: center;
  align-items: center;
}

/* Or a single line with grid */
.center { display: grid; place-items: center; }

2. Two-dimensional layout — Grid > table / nested flex

Bad

css
/* Using <table> or deeply nested flex
   to split into multi-column + multi-row */

Good

css
.layout {
  display: grid;
  grid-template-columns: 1fr 500px 1fr;
  grid-template-rows: 100px 200px;
  place-items: center;
}

3. Center a <div> in the viewport — single block

html
<div class="parent">
  <div>I'm centered</div>
</div>

css
.parent {
  display: grid;
  place-content: center;
  height: 100vh;
}

4. Responsive width — clamp() instead of 3 media queries

Bad

css
article { width: 50%; }

@media (max-width: 600px) {
  article { width: 200px; }
}
@media (min-width: 1200px) {
  article { width: 800px; }
}

Good

css
article {
  /* MIN, Preferred, MAX */
  width: clamp(200px, 50%, 600px);
}

clamp() works great for font-size, padding, gap… This is the “responsive without media queries” approach.

5. Aspect ratio — one line instead of the padding-top hack

Bad

css
.container-16x9 {
  position: relative;
  padding-top: 56.25%;
}
.container-16x9 video {
  position: absolute;
  inset: 0;
  width: 100%;
}

Good

css
video {
  width: 100%;
  aspect-ratio: 16 / 9;
}

6. Variables for variables — CSS custom properties

Bad

css
p  { color: rgb(255, 0, 0); }
h1 { color: rgb(255, 0, 0); }
h2 { color: rgb(255, 0, 0); }

Good

css
:root {
  --r: 255; --g: 0; --b: 0;
  --text-color: rgb(var(--r), var(--g), var(--b));
}

p  { --text-color: green;            /* override */
     color: var(--text-color); }
h1 { color: var(--text-color); }
h2 { color: var(--text-color); }

7. Dark mode with custom properties

css
:root  { --bg: #fff; --fg: #111; }
.dark  { --bg: #111; --fg: #eee; }
body   { background: var(--bg); color: var(--fg); }

To toggle dark mode, just add the class .dark on <html> — no need to change each selector.

8. Logical properties — RTL friendly

css
/* Instead of margin-left/right (physical) */
margin-inline: auto;          /* horizontal, follows writing direction */
padding-block: 1rem;          /* vertical, follows writing direction */
border-inline-start: 2px solid;

Automatically flips when dir="rtl" — no need to write separate CSS.

9. Stagger animation — calc() + custom property

Bad

css
.drop  { animation: dropIn 1s ease forwards; }
.ace   { animation-delay: 100ms; }
.deuce { animation-delay: 200ms; }
.trey  { animation-delay: 300ms; }

@keyframes dropIn {
  from { transform: translateY(-500px); }
  to   { transform: translateY(0); }
}

Good

css
.drop {
  animation: dropIn 1s ease forwards;
  animation-delay: calc(var(--order) * 100ms);
}

@keyframes dropIn {
  from { transform: translateY(-500px); }
  to   { transform: translateY(0); }
}

/* HTML */
/* <i class="drop" style="--order: 1">1</i> */
/* <i class="drop" style="--order: 2">2</i> */
/* <i class="drop" style="--order: 3">3</i> */

10. State — counter() for automatic numbering

Bad

html
<h1>1. Awesome</h1>
<h1>2. Cool</h1>
<h1>3. Radical</h1>

Good

html
/* CSS */
:root { counter-reset: headings; }
h1    { counter-increment: headings; }
h1::before { content: counter(headings) ". "; }

<!-- HTML — no manual numbering needed -->
<h1>Awesome</h1>
<h1>Cool</h1>
<h1>Radical</h1>

11. :focus-within — catch focus of a descendant

Bad

css
.dropdown {
  opacity: 0;
  visibility: hidden;
}

button:focus .dropdown {   /* only catches focus on the button itself */
  opacity: 1;
  visibility: visible;
}

Good

css
.dropdown {
  opacity: 0;
  visibility: hidden;
}

/* Catch focus on ANY child inside the button */
button:focus-within .dropdown {
  opacity: 1;
  visibility: visible;
}

12. :has() — parent selector (now widely supported)

css
/* If a card has an image, reduce its padding */
.card:has(img) { padding: 0.5rem; }

/* If a form has an invalid input, dim the submit button */
form:has(input:invalid) button { opacity: 0.5; }

/* If the body has an open sidebar, push the main content */
body:has(.sidebar.open) main { margin-left: 240px; }

13. Truncate text (single line / multiple lines)

css
/* Single line */
.truncate {
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

/* Multiple lines */
.clamp-3 {
  display: -webkit-box;
  -webkit-line-clamp: 3;
  -webkit-box-orient: vertical;
  overflow: hidden;
}

14. Focus visible — pretty & a11y

Bad

css
button:focus {
  outline: none;   /* breaks a11y, keyboard-tab users get lost */
}

Good

css
button:focus { outline: none; }

/* Only show the outline when the user tabs with the keyboard */
button:focus-visible {
  outline: 2px solid #6366f1;
  outline-offset: 2px;
}

⚠️Don't disable outline without replacing it with another focus state.

15. Smooth scroll & scroll-margin (sticky header)

css
html    { scroll-behavior: smooth; }
section { scroll-margin-top: 5rem; }   /* offset for the sticky header */

16. will-change — use it in the right place

💡Only add will-change RIGHT BEFORE animating, and remove it when done. Overusing it wastes GPU memory unnecessarily.

css
/* Bad: always on for every card */
.card { will-change: transform; }

/* Good: only on when it's about to animate */
.card.is-animating { will-change: transform; }

17. DevTools tip — Firefox > Chrome for debugging layout

Firefox has a more visual Grid Inspector & Flex Inspector than Chrome.
Show grid/flex lines, gaps, and item order with just one click.
Firefox's Font Inspector is also superior for debugging typography.