Sidebar Navigation Menu | HTML, CSS & JavaScript

:root {
      --bg-primary: #111827;
      --bg-secondary: #1f2937;
      --text-main: #f9fafb;
      --text-muted: #9ca3af;
      --accent: #3b82f6;
      --sidebar-width: 280px;
      --transition-speed: 0.35s;
      --transition-curve: cubic-bezier(0.4, 0, 0.2, 1);
    }

* {
      margin: 0;
      padding: 0;
      box-sizing: border-box;
      font-family: 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
    }

body {
      background-color: #f3f4f6;
      color: #111827;
      overflow-x: hidden;
    }

/* --- Hamburger Toggle Button --- */
    .menu-toggle {
      position: fixed;
      top: 20px;
      left: 20px;
      z-index: 100;
      width: 45px;
      height: 45px;
      background-color: var(--bg-primary);
      border: none;
      border-radius: 8px;
      cursor: pointer;
      display: flex;
      flex-direction: column;
      justify-content: center;
      align-items: center;
      gap: 6px;
      transition: background-color var(--transition-speed);
      box-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    }

.menu-toggle:hover {
      background-color: var(--accent);
    }

/* Hamburger Lines */
    .bar {
      width: 24px;
      height: 3px;
      background-color: var(--text-main);
      border-radius: 2px;
      transition: transform var(--transition-speed) var(--transition-curve),
                  opacity var(--transition-speed) var(--transition-curve);
    }

/* Hamburger to 'X' Animation State */
    .menu-toggle.active .bar:nth-child(1) {
      transform: translateY(9px) rotate(45deg);
    }
    .menu-toggle.active .bar:nth-child(2) {
      opacity: 0;
    }
    .menu-toggle.active .bar:nth-child(3) {
      transform: translateY(-9px) rotate(-45deg);
    }

/* --- Sidebar Container --- */
    .sidebar {
      position: fixed;
      top: 0;
      left: 0;
      width: var(--sidebar-width);
      height: 100vh;
      background-color: var(--bg-primary);
      z-index: 90;
      padding: 90px 24px 24px 24px;
      /* GPU Accelerated off-screen translation */
      transform: translateX(-100%); 
      transition: transform var(--transition-speed) var(--transition-curve);
      box-shadow: 4px 0 25px rgba(0, 0, 0, 0.15);
    }

.sidebar.open {
      transform: translateX(0);
    }

/* --- Navigation Links --- */
    .nav-menu {
      list-style: none;
      display: flex;
      flex-direction: column;
      gap: 8px;
    }

.nav-item {
      /* Setup for staggered entrance animation */
      opacity: 0;
      transform: translateX(-20px);
      transition: opacity 0.4s var(--transition-curve), 
                  transform 0.4s var(--transition-curve);
    }

/* When sidebar opens, trigger item transitions */
    .sidebar.open .nav-item {
      opacity: 1;
      transform: translateX(0);
    }

/* Staggered transition delays for buttery-smooth cascade */
    .sidebar.open .nav-item:nth-child(1) { transition-delay: 0.1s; }
    .sidebar.open .nav-item:nth-child(2) { transition-delay: 0.15s; }
    .sidebar.open .nav-item:nth-child(3) { transition-delay: 0.20s; }
    .sidebar.open .nav-item:nth-child(4) { transition-delay: 0.25s; }
    .sidebar.open .nav-item:nth-child(5) { transition-delay: 0.30s; }

.nav-link {
      display: flex;
      align-items: center;
      padding: 14px 16px;
      color: var(--text-muted);
      text-decoration: none;
      font-size: 1.1rem;
      font-weight: 500;
      border-radius: 8px;
      transition: color 0.2s, background-color 0.2s;
    }

.nav-link:hover, .nav-item.active .nav-link {
      color: var(--text-main);
      background-color: var(--bg-secondary);
    }

.nav-link::before {
      content: '';
      width: 6px;
      height: 0;
      background-color: var(--accent);
      position: absolute;
      left: 12px;
      border-radius: 4px;
      transition: height 0.2s ease;
    }

.nav-link:hover::before, .nav-item.active .nav-link::before {
      height: 20px;
    }

/* --- Content Overlay --- */
    .overlay {
      position: fixed;
      top: 0;
      left: 0;
      width: 100vw;
      height: 100vh;
      background-color: rgba(0, 0, 0, 0.4);
      backdrop-filter: blur(4px);
      z-index: 80;
      opacity: 0;
      pointer-events: none;
      transition: opacity var(--transition-speed) ease;
    }

.overlay.show {
      opacity: 1;
      pointer-events: auto;
    }

/* --- Main Content Demo Canvas --- */
    .main-content {
      padding: 40px 40px 40px 90px;
      max-width: 1000px;
      margin: 0 auto;
      transition: padding-left var(--transition-speed) var(--transition-curve);
    }

h1 {
      margin-bottom: 16px;
      font-size: 2.5rem;
    }

p {
      color: #4b5563;
      line-height: 1.6;
    }

- Sidebar Navigation Menu

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