Apa iku pseudo-class lan apa wae sing umum?

Question

Accepted Answer

A **pseudo-class** (titik tunggal `:`) milih elemen adhedhasar **state** utawa **posisi** — samubarang sing ora bisa diepresi nganggo class biasa, kayata "nalika hover" utawa "anak pisanan."

## State pseudo-classes (interaksi)

```css
a:hover    { color: blue; }      /* mouse is over it */
a:focus    { outline: 2px solid; } /* keyboard/tab focus — keep for accessibility! */
button:active   { transform: scale(0.98); } /* while being pressed */
button:disabled { opacity: 0.5; } /* disabled form controls */
input:checked   { } /* checked checkbox/radio */
input:focus-visible { } /* focus only when keyboard-navigating (not mouse) */
```

Urutan kanggo link penting (LVHA): `:link`, `:visited`, `:hover`, `:active`.

## Structural pseudo-classes (posisi)

```css
li:first-child  { } /* first li among its siblings */
li:last-child   { } /* last one */
li:nth-child(2) { } /* the 2nd */
li:nth-child(odd)  { } /* 1st, 3rd, 5th... — zebra striping */
li:nth-child(3n)   { } /* every 3rd */
p:only-child    { } /* a p that's the sole child */
```

`:nth-child()` iku kuat — `2n` (genap), `2n+1` (ganjil), `3n` (saben katelu), etc.

## Form & modern pseudo-classes

```css
input:required  { }
input:invalid   { border-color: red; }
:is(h1, h2, h3) { }  /* matches any — shortens selector lists */
.card:has(img)  { }  /* the "parent selector": a card that CONTAINS an img */
:not(.active)   { }  /* everything except .active */
```

## Pseudo-class vs pseudo-element

Pseudo-class nganggo **siji** titik (`:hover`, *state*); pseudo-element nganggo **loro** (`::before`, *bagean sing dibuat*). Aja nglirwakake.

## Mengapa iku penting

Pseudo-class ndadekke sampeyan bisa nggayani interaksi (hover/focus — penting kanggo UI sing bisa digunakake lan accessible) lan struktur (striping, first/last) tanpa markup tambahan utawa JavaScript.

Nominal modern (`:has`, `:is`, `:focus-visible`) ngrampungake masalah sing sadurunge mbutuhake JS utawa selector sing mbaleni.