What CSS is
CSS (Cascading Style Sheets) describes how HTML elements look. It works through selectors that target one or more elements, and declarations that change a property.
Example
h1 { font-size: 28px; color: #0F6E56; }
.card { padding: 16px; border-radius: 8px; background: #fff; }
.card a:hover { text-decoration: underline; }Key concepts
- Cascade: multiple rules can hit the same element; the most specific or last-declared wins.
- Box model: content, padding, border, margin.
- Specificity: id > class > tag.
- Pseudo-classes:
:hover,:focus,:nth-child().
The most common mistake is assuming !important will fix things — it is usually a symptom of a specificity problem you should understand.