Why is my Bootstrap dropdown menu not working?

The Bootstrap component does not automatically add the aria attributes required for complete WCAG. You need to manually complete aria-expanded, role="dialog", aria-labelledby, etc.; the form must be equipped with an explicit label; :focus needs to use :focus-visible to ensure that the keyboard focus is visible; the color contrast must reach 4.5:1.

The fade and show classes of Bootstrap5 are only status markers and do not contain animation logic. You need to manually add @keyframes or transitions to achieve fade-in and fade-out; custom components need to configure additional animation rules, and when JS controls the display, the show class must be added with delay to ensure redrawing.

Only BootstrapCSS should be introduced in React/Vue instead of JS to avoid global style pollution and jQuery dependency; SCSS modules should be imported on demand to reduce the size; interactive functions must be imported with encapsulation libraries (such as react-bootstrap) or ESM; grid classes need to adapt to JSX/Vue syntax, and explicit and implicit classes should be used with SSR with caution.

Bootstrap’sdefaultstylingfeelsgenericduetouncustomizedspacing,typography,andcolor—fixableviaCSSvariablesorSass,notdirectedits;avoidfixedwidths,misuseofgridclasses,andrender-blockingassetstoensureresponsivenessandfastLCP.

To correctly introduce Bootstrap5, you need to load bootstrap.min.css first, then load bootstrap.bundle.min.js (including Popper), and ensure that the viewport tag exists; after npm installation, you need to manually introduce compiled files in the dist directory. SCSS customization must be preceded by variable declarations, and JS components must be explicitly initialized to avoid jQuery contamination.

Use mt-3 to represent the top margin, mb-3 to represent the bottom margin, and the suffixes t/b/s/e correspond to top/bottom/start/end respectively; ms-auto implements right alignment in the flex container, me-2 replaces the abandoned mr-2, and responsive classes such as mt-md-4 need to have breakpoint prefixes.

The only sidebar solution natively supported by Bootstrap 5 is offcanvas. It defaults to a drawer for small screens and can be resident for large screens. It has backdrop, keyboard close, animation and accessibility support. It needs to use dual structure or JS to dynamically control the responsive display, and customize the width, height and background through CSS variables.

The safest way is to redefine Bootstrap's Sass variables (such as $primary, $primary-rgb, $primary-text-emphasis) in advance and introduce them before @import "bootstrap/scss/variables" to ensure that all dependent variables are updated synchronously to avoid compilation failure or style exceptions.