How to Choose Between Flexbox and CSS Grid

Ask yourself: Is this layout One-Dimensional (just a row, or just a column) or Two-Dimensional (requires rows AND columns simultaneously)?

If aligning items inside a single row (like a Navbar, a toolbar, or a row of tags), choose Flexbox. It excels at 'content-first' design, where the size of the items dictates how they flex and wrap.

If designing a macro page layout (Header, Sidebar, Main Content, Footer) or a complex image gallery, choose CSS Grid. It excels at 'layout-first' design, where you define rigid slots and place items into them.

Understand that 'flex: 1' means the item will grow to fill available space, shrink if necessary, and start with a basis of 0. Using flex: 1 on three items in a row guarantees they split the space exactly 33% each.

Use the 'fr' unit to divide available space effortlessly. 'grid-template-columns: 1fr 2fr 1fr' creates three columns, automatically giving the middle column exactly 50% of the space and the others 25%.

In real-world architecture, you rarely choose just one. Use CSS Grid to define the major structural regions of the page, and use Flexbox inside those regions to perfectly align text, icons, and buttons.