Bootstrap Primary

Bootstrap Primary is the default action color across the framework: links, primary buttons, focused inputs, and active navigation items all default to this blue. It is calibrated to pass WCAG AA against white at standard button heights, which is why it tends to feel slightly darker than fashion-forward blues in newer design systems. Because billions of sessions have trained users to expect this exact hue as the thing to click, replacing it in a Bootstrap codebase requires updating user mental models as well as CSS variables. It is a load-bearing convention rather than a stylistic choice.