Frontend·Beginner·10 questions

CSS

Style, layout, and responsive design — from Flexbox to Grid to animations.

Overview

CSS (Cascading Style Sheets) controls the visual appearance of HTML. You can add CSS in three ways: inline (inside the tag), internal (<style> in <head>), or external (a separate .css file linked with <link>). External CSS is the best practice for maintainability.

Every HTML element is a rectangular box. The CSS Box Model defines four layers: content, padding (inside the border), border, and margin (outside the border). Flexbox and CSS Grid are the modern tools for building layouts. Flexbox is great for one-dimensional layouts (rows OR columns), while Grid handles two-dimensional layouts (rows AND columns simultaneously).

Responsive design ensures your site looks great on all devices. Media queries (@media) let you apply different styles at different screen sizes. CSS also provides powerful selectors (class, id, element, pseudo-classes like :hover and :focus) and the cascade determines which style wins when multiple rules conflict, based on specificity.

Code Example

Flexbox Navbar + Responsive Grid + Hover Animation
css
/* CSS Variables */
:root {
  --primary: #6366f1;
  --text: #1e293b;
  --radius: 0.5rem;
}

/* Flexbox Navbar */
.navbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 1rem 2rem;
  background: white;
  box-shadow: 0 1px 3px rgba(0,0,0,0.1);
}

/* Responsive Card Grid */
.card-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.5rem;
  padding: 2rem;
}

/* Card with hover animation */
.card {
  background: white;
  border-radius: var(--radius);
  padding: 1.5rem;
  border: 1px solid #e2e8f0;
  transition: transform 0.2s ease, box-shadow 0.2s ease;
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 24px rgba(99,102,241,0.15);
}

/* Pseudo-elements */
.card::before {
  content: '';
  display: block;
  height: 4px;
  background: var(--primary);
  border-radius: var(--radius) var(--radius) 0 0;
  margin: -1.5rem -1.5rem 1rem;
}

/* Media Query for Mobile */
@media (max-width: 768px) {
  .navbar {
    flex-direction: column;
    gap: 1rem;
  }
}

/* CSS Animation */
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(10px); }
  to   { opacity: 1; transform: translateY(0); }
}

.card {
  animation: fadeIn 0.3s ease forwards;
}

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