Structure and style meet
The browser reads HTML into a document tree and CSS into styling rules. It combines the visible parts, calculates their sizes and positions, and prepares layers that can be drawn.
Scripts can change the result
JavaScript may add content, respond to data, or change classes and attributes. Those changes can require new style, layout, and paint work, which is why the order and size of page resources affect what appears first.
A familiar example
Showing a news homepage
- HTML provides headings, links, and article structure.
- CSS turns that structure into columns, spacing, colors, and readable type.
- JavaScript adds live behavior such as a menu or refreshed headlines.
What to remember
- HTML provides structure, CSS presentation, and JavaScript behavior.
- Layout decides geometry before paint draws pixels.
- Early useful content should not wait for unnecessary scripts.