4. CSS Units

Explanation: Jab bhi hum kisi element ko size, margin, padding, ya font-size dete hain CSS mein, to humein UNIT lagani padti hai. Jaise 10px, 50%, 2em, 100vw, etc. Unit batata hai ki value ka scale kya hoga.

I. Absolute Units

Definition: Ye fixed hote hain, screen ya parent size se nahi badalte. Har jagah same dikhte hain.

px (pixels): Sabse commonly used unit. Ek pixel = screen ka ek point.
cm (centimeter), mm (millimeter), in (inch): Real world units — print media mein use hote hain.

Use: Jab hume exact control chahiye layout par, jaise border, box size, buttons, etc.

II. Relative Units

Definition: Ye apne parent element ya default font size ke basis par kaam karte hain.

% (percentage): Parent element ke size ka percentage.
em: Current element ke font-size ke base par (1em = current font size).
rem (root em): Root element (HTML tag) ke font-size ke base par.

Use: Responsive design ke liye best — screen ke size ke hisaab se adjust hota hai.

III. Viewport Units

Definition: Ye screen ke viewport (visible area) ke hisaab se size dete hain. Super useful in responsive layout.

vw (viewport width): 1vw = 1% of browser width
vh (viewport height): 1vh = 1% of browser height
vmin, vmax: Minimum ya maximum of vw and vh

Use: Full screen layouts, banners, headers banane ke liye perfect.