:root {
  --bg-color: #000000;
  --text-primary: #ffffff;
  --text-secondary: #aaaaaa;
  --accent-color: #ff2c55; /* TikTok/Kwai style vibrant red */
  --nav-bg: rgba(0, 0, 0, 0.85);
}

:root.light-mode {
  --bg-color: #ffffff;
  --text-primary: #000000;
  --text-secondary: #555555;
  --nav-bg: rgba(255, 255, 255, 0.9);
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body, html {
  width: 100%;
  height: 100%;
  background-color: var(--bg-color);
  color: var(--text-primary);
  font-family: 'Inter', -apple-system, sans-serif;
  overflow: hidden; /* App-like feel, no standard scrolling */
}

/* App Shell Layout */
#app-container {
  display: flex;
  flex-direction: column;
  height: 100vh;
}

/* Navbar */
.top-navbar {
  position: absolute;
  top: 0;
  width: 100%;
  padding: 15px 20px;
  display: flex;
  justify-content: center;
  gap: 20px;
  z-index: 100;
  background: linear-gradient(to bottom, rgba(0,0,0,0.6) 0%, rgba(0,0,0,0) 100%);
}

.top-navbar span {
  font-size: 1.1rem;
  font-weight: 600;
  opacity: 0.6;
  cursor: pointer;
  transition: opacity 0.2s;
}

.top-navbar span.active {
  opacity: 1;
  border-bottom: 2px solid var(--text-primary);
  padding-bottom: 5px;
}

/* Main Content Area */
#main-feed {
  flex: 1;
  position: relative;
  background: #111;
}

/* Bottom Bar */
.bottom-bar {
  position: absolute;
  bottom: 0;
  width: 100%;
  height: 60px;
  background-color: var(--nav-bg);
  backdrop-filter: blur(10px);
  display: flex;
  justify-content: space-around;
  align-items: center;
  border-top: 1px solid rgba(255,255,255,0.1);
  z-index: 100;
}

.nav-item {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 4px;
  color: var(--text-secondary);
  font-size: 0.75rem;
  cursor: pointer;
}

.nav-item.active {
  color: var(--text-primary);
}

.add-button {
  width: 45px;
  height: 30px;
  background: linear-gradient(45deg, #20D5EC, var(--accent-color));
  border-radius: 8px;
  display: flex;
  justify-content: center;
  align-items: center;
  color: white;
  font-weight: bold;
  font-size: 1.2rem;
}

/* Theme Toggle Button */
.theme-toggle {
  position: absolute;
  top: 15px;
  right: 20px;
  background: none;
  border: none;
  color: var(--text-primary);
  font-size: 1.5rem;
  z-index: 200;
  cursor: pointer;
  opacity: 0.8;
}
.theme-toggle:active {
  transform: scale(0.9);
}