:root {
  /* Animation Easings */
  --ease-out-back: cubic-bezier(0.34, 1.56, 0.64, 1);
  --font-sans:
    "Source Sans 3", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    sans-serif;

  /* Corner Radii */
  --radius-s: 4px;
  --radius-m: 6px;
  --radius-l: 12px;
  --radius-xl: 0.5rem; /* For cards */
  --radius-pill: 9999px;

  /* Spacing Gaps */
  --gap-s: 0.25rem;
  --gap-m: 0.5rem;
  --gap-l: 0.75rem;
  --gap-xl: 1rem;
  --gap-2xl: 1.5rem;

  /* Base Palette */
  --slate-200: #e2e8f0;
  --slate-400: #94a3b8;
  --slate-500: #64748b;
  --slate-700: #334155;
  --slate-800: #1e293b;
  --slate-900: #0f172a;
  --yellow-400: #facc15;
  --orange-400: #fb923c;
  --orange-500: #f97316;
  --red-500: #ef4444;
  --sky-200: #bae6fd;
  --sky-400: #38bdf8;
  --sky-500: #0ea5e9;
  --white: #ffffff;

  /* Default Theme: Dark Mode */
  --bg-gradient: radial-gradient(ellipse at bottom, #1b2735 0%, #090a0f 100%);
  --bg-color: #090a0f;
  --text-main: #f0f0f2;
  --text-muted: var(--slate-400);
  --text-heading: #ffffff;
  --accent: #3b82f6;
  --h1-start: #ffffff;

  --card-bg: var(--slate-800);
  --card-bg-frosted: rgba(255, 255, 255, 0.05);
  --card-border: transparent;
  --card-border-frosted: rgba(255, 255, 255, 0.1);
  --card-shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);

  --input-bg: #111;
  --input-border: #333;

  /* Streak specific shared vars */
  --color-success: hsl(200, 80%, 62%);
  --color-star-bg: var(--slate-700);
  --color-freeze-icon: var(--white);
  --color-background-alt: var(--slate-900);
  --color-background-secondary: var(--slate-700);
  --color-checkpoint-icon: var(--slate-900);
}

/* Light Mode Overrides */
html.force-light-mode {
  --bg-gradient: none;
  --bg-color: #ffffff;
  --text-main: #0f172a;
  --text-muted: var(--slate-500);
  --text-heading: #0f172a;
  --h1-start: #1e293b;

  --card-bg: var(--white);
  --card-bg-frosted: rgba(15, 23, 42, 0.05);
  --card-border: var(--slate-200);
  --card-border-frosted: rgba(15, 23, 42, 0.1);

  --input-bg: #f1f5f9;
  --input-border: #cbd5e1;

  --color-success: hsl(200, 80%, 38%);
  --color-star-bg: var(--slate-200);
  --color-freeze-icon: var(--sky-200);
  --color-background-alt: hsl(200, 30%, 97%);
  --color-background-secondary: hsl(200, 20%, 90%);
  --color-checkpoint-icon: var(--white);
}

/* System Preference Support */
@media (prefers-color-scheme: light) {
  :root:not(.force-dark-mode) {
    --bg-gradient: none;
    --bg-color: #ffffff;
    --text-main: #0f172a;
    --text-muted: var(--slate-500);
    --text-heading: #0f172a;
    --h1-start: #1e293b;

    --card-bg: var(--white);
    --card-bg-frosted: rgba(15, 23, 42, 0.05);
    --card-border: var(--slate-200);
    --card-border-frosted: rgba(15, 23, 42, 0.1);

    --input-bg: #f1f5f9;
    --input-border: #cbd5e1;

    --color-success: hsl(200, 80%, 38%);
    --color-star-bg: var(--slate-200);
    --color-freeze-icon: var(--sky-200);
    --color-background-alt: hsl(200, 30%, 97%);
    --color-background-secondary: hsl(200, 20%, 90%);
    --color-checkpoint-icon: var(--white);
  }
}

/* Global Reset & Base Styles */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  font-weight: normal;
}

html {
  line-height: 1.4;
  font-family: var(--font-sans);
  text-rendering: optimizeLegibility;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  color: var(--text-main);
  background: var(--bg-color);
}

body {
  margin: 0;
  padding: 0;
  min-height: 100svh;
  background-color: var(--bg-color);
  background-image: var(--bg-gradient);
  transition:
    background-color 0.3s ease,
    color 0.3s ease;
}

h1,
h2,
h3 {
  line-height: 1.2;
  font-weight: 900;
  margin: 0;
  color: var(--text-heading);
}

/* Shared Components: Cards */
.card {
  background-color: var(--card-bg);
  border: 1px solid var(--card-border);
  border-radius: var(--radius-l);
  padding: 1.5rem;
  color: var(--text-main);
  overflow: hidden;
  box-shadow: var(--card-shadow);
  width: 60%;
  max-width: 500px;
  margin: 0 auto var(--gap-xl) auto;
}

.card.frosted {
  background-color: var(--card-bg-frosted);
  border-color: var(--card-border-frosted);
  backdrop-filter: blur(10px);
}

/* Icons */
.material-symbols-outlined {
  font-variation-settings:
    "FILL" 0,
    "wght" 400,
    "GRAD" 0,
    "opsz" 24;
  display: flex;
  align-items: center;
  justify-content: center;
  line-height: 1;
}

/* Theme Toggle Component */
.top-nav {
  position: fixed;
  top: 0;
  right: 0;
  padding: 1rem;
  z-index: 100;
  display: flex;
  gap: 0.5rem;
}

.theme-toggle,
#logout-btn {
  appearance: none;
  background: none;
  border: none;
  color: var(--text-main);
  cursor: pointer;
  padding: 0.5rem;
  display: flex;
  align-items: center;
  justify-content: center;
}

.theme-toggle .sun,
.theme-toggle .moon {
  display: none;
}

/* Initial display logic */
.theme-toggle .moon {
  display: flex;
}
@media (prefers-color-scheme: dark) {
  .theme-toggle .moon {
    display: none;
  }
  .theme-toggle .sun {
    display: flex;
  }
}
html.force-light-mode .theme-toggle .moon {
  display: flex;
}
html.force-light-mode .theme-toggle .sun {
  display: none;
}
html.force-dark-mode .theme-toggle .moon {
  display: none;
}
html.force-dark-mode .theme-toggle .sun {
  display: flex;
}

/* Utilities */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border-width: 0;
}

/* Global Element Defaults */
a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 600;
  transition: opacity 0.2s ease;
}

a:hover {
  opacity: 0.8;
}

input {
  font: inherit;
  padding: 0.8rem;
  border-radius: var(--radius-m);
  border: 1px solid var(--input-border);
  background: var(--input-bg);
  color: var(--text-main);
  transition: border-color 0.2s ease;
}

input:focus {
  outline: none;
  border-color: var(--accent);
}

button {
  font: inherit;
  background: var(--accent);
  color: white;
  border: none;
  padding: 0.8rem 1.5rem;
  border-radius: var(--radius-m);
  font-weight: 600;
  cursor: pointer;
  transition:
    filter 0.2s ease,
    transform 0.1s ease;
}

button:hover {
  filter: brightness(1.1);
}

button:active {
  transform: scale(0.98);
}

button:disabled {
  cursor: not-allowed;
  opacity: 0.5;
  filter: none;
}