Why do spacing, alignment, and a simple grid make interfaces look more professional?

A spacing scale (4, 8, 12, 16, 24, 32, …) means you repeat the same handful of gaps and paddings, so the eye stops measuring random pixels. Alignment to a common grid and baseline makes columns and form fields line up, which people read as 'designed' rather than 'pasted'. More whitespace is not 'waste': it groups related things and separates sections. Tight, uneven padding around cards or buttons is one of the fastest tells of a rough mock.

/* spacing tokens as multiples of 4 or 8 */
.gap-2 { gap: 0.5rem; }  /* 8px if 1rem=16px */
.p-4  { padding: 1rem; }

Start simple: try this concept in a tiny project before moving to advanced tools.