/* ==========================================================================
   base.css — Core styles for Django project
   Author: Your Name
   Last updated: 2025
   ========================================================================== */

/* --------------------------------------------------------------------------
   1. CSS Custom Properties (Design Tokens)
   -------------------------------------------------------------------------- */

:root {
  /* Colors */
  --color-primary:        #B22222;   /* Firebrick — main brand */
  --color-primary-dark:   #800000;   /* Maroon    — accents, borders */
  --color-secondary:      #A52A2A;   /* Brown     — headings */
  --color-link:           #000080;   /* Navy      — nav & button text */
  --color-link-article:   #0000CD;   /* MediumBlue — body links */
  --color-footer-link:    #B22222;
  --color-text:           #333333;
  --color-text-muted:     #666666;
  --color-text-placeholder: #999999;
  --color-bg-page:        #f4f4f4;
  --color-bg-card:        #ffffff;
  --color-bg-input:       #FFFFE0;
  --color-bg-button:      #F5F5F5;
  --color-border:         #04699d;
  --color-footnote:       #888888;
  --color-bg-submit:       #F0FFFF;   /* Azure     — submit button bg */
  --color-bg-table-header: #f2f2f2;   /* Light grey — table th bg */
  --color-border-table:    #dddddd;   /* Light grey — table cell border */

  /* Typography */
  --font-family-base:     'Arial', sans-serif;
  --font-size-base:       1rem;       /* 16px */
  --line-height-base:     1.6;

  /* Spacing */
  --space-xs:  0.25rem;   /*  4px */
  --space-sm:  0.5rem;    /*  8px */
  --space-md:  1rem;      /* 16px */
  --space-lg:  1.25rem;   /* 20px */
  --space-xl:  2rem;      /* 32px */

  /* Layout */
  --container-max-width:  800px;
  --container-min-width:  320px;

  /* Borders & Shadows */
  --radius-sm:      4px;
  --radius-md:      5px;
  --shadow-card:    0 0 10px rgba(0, 0, 0, 0.1);
}

/* --------------------------------------------------------------------------
   2. Box Model Reset
   -------------------------------------------------------------------------- */

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

/* --------------------------------------------------------------------------
   3. Base / Body
   -------------------------------------------------------------------------- */

html {
  font-size: 100%; /* Respects user's browser font size preference */
  scroll-behavior: smooth;
}

body {
  font-family: var(--font-family-base);
  font-size: var(--font-size-base);
  line-height: var(--line-height-base);
  background-color: var(--color-bg-page);
  color: var(--color-text);
  padding: var(--space-sm);
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

/* --------------------------------------------------------------------------
   4. Layout — Container
   -------------------------------------------------------------------------- */

.container {
  flex: 1;
  display: flex;
  flex-direction: column;
  width: 100%;
  max-width: var(--container-max-width);
  min-width: var(--container-min-width);
  margin: 0 auto;
  padding: var(--space-lg);
  background: var(--color-bg-card);
  box-shadow: var(--shadow-card);
}

/* --------------------------------------------------------------------------
   5. Navigation
   -------------------------------------------------------------------------- */

nav {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding-bottom: var(--space-sm);
  margin-bottom: 0;
  border-bottom: 1px solid var(--color-primary-dark);
}

nav ul {
  list-style: none;
  display: flex;
  gap: var(--space-sm); /* replaces margin-right on li */
}

nav a {
  text-decoration: none;
  color: var(--color-link);
}

nav a:hover,
nav a:focus-visible {
  text-decoration: underline;
}

/* --------------------------------------------------------------------------
   6. Header
   -------------------------------------------------------------------------- */

header {
  margin-top: var(--space-lg);
  margin-bottom: var(--space-sm);
  text-align: center;
}

header h1 {
  font-size: 1.6em;
  color: var(--color-primary);
}

header p {
  font-size: 1.1em;
  color: var(--color-text-muted);
}

/* --------------------------------------------------------------------------
   7. Main Content
   -------------------------------------------------------------------------- */

main {
  flex: 1;
  margin-bottom: var(--space-lg);
}

/* --------------------------------------------------------------------------
   8. Article / Post
   -------------------------------------------------------------------------- */

article {
  margin-bottom: var(--space-lg);
}

article:last-child {
  margin-bottom: 0;
}

article h2 {
  font-size: 1.5em;
  color: var(--color-secondary);
  margin-top: var(--space-lg);
  margin-bottom: var(--space-sm);
}

article h3 {
  font-size: 1.2em;
  margin-top: var(--space-lg);
  margin-bottom: var(--space-sm);
}

article p {
  margin-bottom: var(--space-sm);
}

article hr {
  margin-top: var(--space-md);
}

article img {
  max-width: 100%;
  height: auto;
  display: block;
  margin: 0 auto;
}

article ul li,
article ol li {
  margin-left: 2em;
}

article a {
  color: var(--color-link-article);
  text-decoration: none;
  margin-right: var(--space-sm);
}

article a:hover,
article a:focus-visible {
  text-decoration: underline;
}

/* --------------------------------------------------------------------------
   9. Standalone h3 (outside article)
   -------------------------------------------------------------------------- */

h3 {
  font-size: 1.3em;
  margin-bottom: var(--space-sm);
}

/* --------------------------------------------------------------------------
   10. Forms — Inputs & Buttons
   -------------------------------------------------------------------------- */

input {
  width: 12em;
  padding: var(--space-xs) var(--space-sm);
  margin: 0 var(--space-sm) var(--space-sm) 0;
  background: var(--color-bg-input);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: inherit;
  font-family: inherit; /* prevent browser default override */
  transition: border-color 0.2s ease, box-shadow 0.2s ease;
}

input:focus {
  outline: none;
  border-color: var(--color-link);
  box-shadow: 0 0 0 2px rgba(0, 0, 128, 0.15);
}

input::placeholder {
  font-size: 0.8em;
  color: var(--color-text-placeholder);
}

button {
  padding: var(--space-xs) var(--space-sm);
  background: var(--color-bg-button);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  font-size: inherit;
  font-family: inherit;
  color: var(--color-link);
  cursor: pointer;
  transition: background-color 0.2s ease;
}

button:hover {
  background-color: #e8e8e8;
}

button:focus-visible {
  outline: 2px solid var(--color-border);
  outline-offset: 2px;
}

/* --------------------------------------------------------------------------
   11. Footer
   -------------------------------------------------------------------------- */

footer {
  text-align: center;
  padding-top: var(--space-sm);
  margin-top: var(--space-lg);
  border-top: 1px solid var(--color-primary-dark);
}

footer p {
  font-size: 0.9em;
  color: var(--color-text-muted);
}

footer p a {
  margin-right: var(--space-sm);
  color: var(--color-footer-link);
  text-decoration: none;
}

footer p a:hover,
footer p a:focus-visible {
  text-decoration: underline;
}

/* --------------------------------------------------------------------------
   12. Utility — Footnote
   -------------------------------------------------------------------------- */

.footnote {
  font-size: 0.8em;
  line-height: 2;
  color: var(--color-footnote);
}

.footnote ul {
  margin-left: 2em;
}

/* --------------------------------------------------------------------------
   13. Shared calc-page utilities
   -------------------------------------------------------------------------- */

/* h1 link used in calc page headers */
header h1 a {
  text-decoration: none;
  color: var(--color-primary);
}

/* Indented formula line */
.formula {
  margin-left: 2.5rem;
}

/* --------------------------------------------------------------------------
   14. Responsive Design
   -------------------------------------------------------------------------- */

@media (max-width: 480px) {
  body {
    padding: var(--space-xs);
  }

  .container {
    padding: var(--space-md);
  }

  nav {
    flex-direction: column;
    align-items: flex-start;
    gap: var(--space-xs);
  }

  nav ul {
    flex-wrap: wrap;
  }

  header h1 {
    font-size: 1.4em;
  }

  header p {
    font-size: 1em;
  }

  article h2 {
    font-size: 1.3em;
  }

  input {
    width: 100%;
  }
}

@media (max-width: 300px) {
  nav ul {
    flex-direction: column;
  }
}