Some CSS you write from memory. Some CSS you should just drag a slider for, because getting it pixel-perfect by editing numbers and refreshing is a bad use of your afternoon. Here are five that earn a bookmark.
Gradients
Linear and radial gradients look simple until you're trying to get three color stops to transition smoothly at exactly the angle you want. The CSS Gradient Generator gives you a live preview with draggable stops and instantly copyable output — faster than eyeballing hex codes in DevTools.
Box shadows
A good shadow is the difference between a card that looks "designed" and one that looks flat, but the offset/blur/spread/opacity combination that looks right is almost never your first guess. The Box Shadow Generator lets you dial in all four values against a live preview, including inset shadows.
Border radius
Perfectly uniform rounded corners are one line of CSS. A shape with four different corner radii — for that organic, blob-like card style — is four numbers you'll be nudging back and forth. The Border Radius Generator handles both, with a toggle to link all corners together when you just want a simple rounded box.
Buttons
Padding, radius, shadow, border, font size — a polished button is six or seven properties working together, and small changes to any one of them change how all the others read. The CSS Button Generator lets you tune the whole thing visually and copy the finished .button { } rule.
Grid layouts
grid-template-columns: repeat(3, 1fr) is easy. Remembering the exact syntax for asymmetric columns, row gaps, and template areas six months later is not. The CSS Grid Generator visualizes your column/row count and gap settings live, so you can see the layout before you commit to the code.
One more for the toolbox
While you're there, the PX to REM Converter is worth bookmarking too — converting design-handoff pixel values to rem by hand is exactly the kind of arithmetic that's easy to get wrong at 5pm on a Friday.
None of these replace understanding CSS. They just remove the "adjust, refresh, adjust, refresh" loop for the properties where the right value is genuinely easier to see than to calculate.