/* ========== C01: PAGE DEFAULTS ==========
   The universal selector includes padding and borders in declared widths.
   Body typography is inherited. rem is relative to the root font size. */
* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: 'DM Sans', Arial, sans-serif;
  color: #172b42;
  background: #fff;
  line-height: 1.65;
}

h1, h2, h3 {
  line-height: 1.15;
}

h1 {
  font-size: 3rem;
  letter-spacing: -0.04em;
  margin: 0 0 1rem;
}

h2 {
  font-size: 2rem;
}

h3 {
  font-size: 1.25rem;
}

p {
  max-width: 65ch;
}

a {
  color: #155a9c;
  text-underline-offset: 0.2em;
}

a:hover {
  color: #943617;
}

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

button, input, select, textarea {
  font: inherit;
}

button, summary {
  cursor: pointer;
}

/* ========== C02: SHARED PAGE SHELL (COPIED FOR INDEPENDENCE) ==========
   .container centers content with auto margins. Flexbox arranges navigation.
   This block is deliberately repeated in each page CSS: no hidden imports. */
.container {
  width: 90%;
  max-width: 1120px;
  margin: 0 auto;
}

.site-header {
  border-bottom: 1px solid #dbe3eb;
  background: white;
}

.header-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.2rem 0;
  flex-wrap: wrap;
}

.brand {
  font-size: 1.2rem;
  font-weight: 700;
  text-decoration: none;
  color: #172b42;
}

.brand ion-icon {
  color: #c04e28;
  vertical-align: middle;
  font-size: 1.5rem;
}

nav ul {
  display: flex;
  flex-wrap: wrap;
  gap: 1.2rem;
  list-style: none;
  padding: 0;
  margin: 0;
}

nav a {
  color: inherit;
  text-decoration: none;
  font-size: 0.95rem;
}

nav a[aria-current='page'] {
  color: #a93917;
  border-bottom: 2px solid currentColor;
}

main {
  min-height: 65vh;
}

section {
  padding: 2.5rem 0;
}

.page-heading {
  padding: 3.5rem 0 1rem;
}

.eyebrow {
  color: #a93917;
  font-size: 0.85rem;
  font-weight: 700;
  letter-spacing: 0.13em;
  text-transform: uppercase;
}

.lead {
  font-size: 1.2rem;
  color: #42586e;
}

.site-footer {
  background: #102d49;
  color: white;
  padding: 2.5rem 0;
  margin-top: 3rem;
}

.site-footer a {
  color: #d7e9fa;
}

.footer-links {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

/* ========== C03: BASIC REUSABLE ELEMENTS ==========
   A class can style many elements. Padding is inside; margin is outside.
   Use a link for navigation and a button for an action. */
.button, button {
  display: inline-block;
  background: #174f7e;
  color: white;
  padding: 0.7rem 1.2rem;
  border: 1px solid #174f7e;
  border-radius: 4px;
  text-decoration: none;
}

.button:hover, button:hover {
  background: #113b60;
  color: white;
}

.secondary {
  color: #174f7e;
  background: white;
}

.cards {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1.5rem;
}

.card {
  border: 1px solid #dbe3eb;
  border-radius: 6px;
  overflow: hidden;
  background: white;
}

.card-body {
  padding: 1.25rem;
}

.card img {
  width: 100%;
  height: 200px;
  object-fit: cover;
}

.note {
  background: #eef5fa;
  border-left: 4px solid #276493;
  padding: 1rem;
}

.tag {
  display: inline-block;
  font-size: 0.85rem;
  background: #edf3f8;
  padding: 0.2rem 0.6rem;
  border-radius: 3px;
}

/* ========== C04: KEYBOARD ACCESS ==========
   :focus-visible makes keyboard focus clear. The skip link appears on focus. */
a:focus-visible, button:focus-visible, input:focus-visible, select:focus-visible, textarea:focus-visible, summary:focus-visible {
  outline: 3px solid #bd481e;
  outline-offset: 4px;
}

.skip-link {
  position: absolute;
  left: 1rem;
  top: -100px;
  background: white;
  padding: 0.8rem;
  z-index: 10;
}

.skip-link:focus {
  top: 1rem;
}

/* ========== C10: COLOUR AND BACKGROUNDS ==========
   TEACH: Compare named colours, HEX, RGB/RGBA and HSL/HSLA. Background layers paint front to back. */
.swatches {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

.swatches span {
  padding: 1rem;
  border: 2px solid currentColor;
}

.named {
  color: navy;
  background-color: transparent;
}

.hex {
  background: #e5efff;
  color: #123456;
}

.rgb {
  background: rgba(20, 90, 170, 0.15);
  color: rgb(20, 60, 100);
}

.hsl {
  background: hsla(210, 60%, 90%, 0.8);
  color: hsl(210, 65%, 25%);
}

.background-demo {
  color: #102d49;
  padding: 2rem;
  border: 8px dashed #7890a5;
  margin-top: 1rem;
  background-image: linear-gradient(#ffffffcc, #ffffffcc), url('../assets/placeholder.png');
  background-size: cover, 200px auto;
  background-repeat: no-repeat, repeat;
  background-position: center;
  background-attachment: scroll;
  background-origin: padding-box;
  background-clip: border-box;
}

/* ========== C11: BOX MODEL AND MARGIN COLLAPSE ==========
   TEACH: Inspect content, padding, border, margin and outline in DevTools. Adjacent vertical block margins can collapse. */
.box-demo {
  width: 260px;
  max-width: 100%;
  min-height: 80px;
  padding: 20px;
  margin: 20px;
  border-style: solid dashed;
  border-width: 3px;
  border-color: #174f7e;
  border-left: 8px solid #bd481e;
  border-radius: 12px;
  outline: 2px dotted #174f7e;
  outline-offset: 5px;
  background: #edf4fa;
}

.collapse-demo {
  display: flow-root;
}

.collapse-demo p:first-child {
  margin-bottom: 30px;
}

.collapse-demo p + p {
  margin-top: 20px;
}

/* ========== C12: TYPOGRAPHY AND TEXT EFFECTS ==========
   TEACH: Test alignment, decoration, transformation, spacing, font fallback, wrapping and truncation. */
.type-demo {
  font: italic 700 1.3rem/1.8 Georgia, 'Times New Roman', serif;
  text-align: center;
  text-decoration: underline dotted #bd481e 2px;
  text-transform: uppercase;
  text-indent: 1em;
  letter-spacing: 0.06em;
  word-spacing: 0.2em;
  text-shadow: 1px 2px 2px #ccd8e2;
}

.ellipsis {
  width: 220px;
  max-width: 100%;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.word-wrap {
  width: 220px;
  overflow-wrap: anywhere;
  word-break: normal;
}

/* ========== C13: SELECTORS AND CASCADE ==========
   TEACH: Compare descendant, child, adjacent sibling and general sibling selectors. Inspect a deliberately scoped !important. */
.selector-demo {
  color: #174f7e;
}

.selector-demo p {
  padding: 0.5rem;
}

.selector-demo > p {
  border-left: 2px solid currentColor;
}

.notice + p {
  background: #edf4fa;
}

.notice ~ p {
  font-style: italic;
}

[data-kind] {
  border-radius: 3px;
}

[data-kind='travel-tip'] {
  font-weight: bold;
}

[data-kind^='travel'] {
  letter-spacing: 0.02em;
}

[data-kind$='tip'] {
  text-decoration: underline;
}

[data-kind*='vel'] {
  padding-right: 1rem;
}

[data-label~='guide'] {
  text-decoration-style: dotted;
}

[data-kind|='travel'] {
  border-top: 1px solid currentColor;
}

#cascade-example {
  color: #174f7e;
}

.selector-demo .notice {
  color: #a93917 !important;
}

/* Demonstration only: avoid routine !important use. */
.selector-demo a {
  color: inherit;
}

.selector-demo p::first-letter {
  font-size: 1.4em;
}

.selector-demo p::selection {
  background: #ffe7c6;
}

/* ========== C14: DISPLAY, POSITION AND OVERFLOW ==========
   TEACH: Compare none with hidden, inline-block with block, and absolute positioning relative to a parent. */
.position-demo {
  position: relative;
  padding: 3rem 1rem 1rem;
  border: 1px solid #ccd8e2;
}

.position-badge {
  position: absolute;
  top: 0.5rem;
  right: 0.5rem;
  z-index: 1;
  background: #edf4fa;
  padding: 0.3rem;
}

.inline-demo {
  display: inline-block;
  width: 120px;
  vertical-align: middle;
}

.invisible {
  visibility: hidden;
}

.removed {
  display: none;
}

.overflow-demo {
  height: 90px;
  overflow-y: auto;
  overflow-x: hidden;
  border: 1px solid #174f7e;
  margin-top: 1rem;
}

/* ========== C15: FLOAT AND CLEAR ==========
   TEACH: Float is useful for wrapping text around an image; use Flexbox or Grid for most page layouts. */
.float-demo img {
  float: left;
  width: 130px;
  margin: 0 1rem 1rem 0;
}

.float-demo::after {
  content: '';
  display: table;
  clear: both;
}

.clear-demo {
  clear: both;
}

/* ========== C16: GRADIENTS, BORDERS AND SHADOWS ==========
   TEACH: Gradients are generated CSS images; border-image can use a gradient or an image. */
.effects-row {
  display: flex;
  flex-wrap: wrap;
  gap: 1rem;
}

.effects-row > div {
  width: 160px;
  height: 100px;
  padding: 1rem;
  color: #102d49;
  border-radius: 10px;
  box-shadow: 3px 4px 10px #0002;
}

.linear {
  background: linear-gradient(90deg, #e5efff, #f8dbb9);
}

.radial {
  background: radial-gradient(circle, #fff, #9dbbdb);
}

.conic {
  background: conic-gradient(#cddff4, #f8dbb9, #cddff4);
}

.border-image {
  border: 10px solid transparent;
  border-image: linear-gradient(90deg, #174f7e, #bd481e) 1;
  padding: 1rem;
}

/* ========== C17: TRANSFORMS, TRANSITIONS AND ANIMATION ==========
   TEACH: Hover or focus the tile. Transform changes appearance without reflow. Reduced-motion preferences disable motion. */
.transform-tile {
  width: 190px;
  padding: 2rem;
  background: #edf4fa;
  transform: translate(5px, 0) rotate(-2deg);
  transition: transform 0.4s ease-in-out 0.1s;
}

.transform-tile:hover, .transform-tile:focus {
  transform: scale(1.05) skew(3deg, 0deg);
}

.motion-dot {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: #bd481e;
  margin-top: 2rem;
  animation: travel 2s ease-in-out 0s 2 alternate both;
}

@keyframes travel {
  from {
    transform: translateX(0);
  }

  to {
    transform: translateX(120px);
  }

}

@media (prefers-reduced-motion: reduce) {
  .motion-dot {
    animation: none;
  }

  .transform-tile {
    transition: none;
  }

}

/* ========== C18: TOOLTIP AND DROPDOWN ==========
   TEACH: Hover and focus-within reveal the tooltip. Native details provides an accessible click/touch dropdown. */
.tooltip-wrap {
  position: relative;
  display: inline-block;
}

.tooltip {
  visibility: hidden;
  opacity: 0;
  position: absolute;
  bottom: 115%;
  left: 0;
  width: 210px;
  background: #102d49;
  color: white;
  padding: 0.5rem;
  border-radius: 4px;
}

.tooltip::after {
  content: '';
  position: absolute;
  top: 100%;
  left: 20px;
  border: 6px solid transparent;
  border-top-color: #102d49;
}

.tooltip-wrap:hover .tooltip, .tooltip-wrap:focus-within .tooltip {
  visibility: visible;
  opacity: 1;
}

.dropdown {
  margin-top: 1rem;
  max-width: 260px;
  border: 1px solid #ccd8e2;
  padding: 1rem;
}

.dropdown ul {
  padding-left: 1.2rem;
}

/* ========== C19: IMAGE SHAPES, MASKS AND SPRITES ==========
   TEACH: The same placeholder is cropped, filtered and masked. A sprite shows different areas of one background image. */
.effects-row img {
  width: 160px;
  height: 120px;
  object-fit: cover;
  object-position: 60% 50%;
}

.overlay-photo {
  position: relative;
  padding: 0 !important;
  overflow: hidden;
}

.overlay-photo span {
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  color: white;
  background: #102d49;
  opacity: 0;
}

.overlay-photo:hover span {
  opacity: 1;
}

.circle-photo {
  clip-path: circle(45%);
  filter: sepia(80%);
}

.masked-photo {
  mask-image: linear-gradient(black, transparent);
}

.sprite {
  display: inline-block;
  width: 80px;
  height: 80px;
  background-image: url('../assets/placeholder.png');
  background-size: 160px 80px;
}

.sprite-left {
  background-position: 0 0;
}

.sprite-right {
  background-position: -80px 0;
}

/* ========== C20: VARIABLES, MATH AND FEATURE QUERIES ==========
   TEACH: Custom properties reuse values; var provides a fallback. Math sets fluid sizes. @supports enables an enhancement. */
@property --panel-accent {
  syntax: '<color>';
  inherits: false;
  initial-value: #174f7e;
}

.variable-demo {
  --space: 1rem;
  --panel-accent: #174f7e;
  padding: var(--space, 16px);
  border: 3px solid var(--panel-accent);
  width: min(100%, 600px);
  min-height: max(80px, 5rem);
}

.variable-demo p {
  width: calc(100% - 1rem);
  font-size: clamp(1rem, 2vw, 1.4rem);
}

@supports (border-radius: 12px) {
  .variable-demo {
    border-radius: 12px;
  }

}

@media (max-width: 700px) {
  .variable-demo {
    --space: 0.75rem;
  }

}

.nested-counter, .nested-counter div {
  counter-reset: part;
}

.nested-counter div::before {
  counter-increment: part;
  content: counters(part, '.') ' ';
}

.nested-counter div {
  margin-left: 1rem;
}

/* ========== C21: CUSTOM FONT AND ERROR INSPECTION ==========
   TEACH: A local font face tries an installed Arial font. Use DevTools to find the intentionally invalid value in this isolated rule. */
@font-face {
  font-family: 'Classroom Local';
  src: local('Arial');
}

.custom-font {
  font-family: 'Classroom Local', Arial, sans-serif;
}

.error-demo {
  color: not-a-color;
}

/* Intentional lesson error; browser ignores only this declaration. */
.resize-demo {
  resize: both;
  overflow: auto;
  width: 260px;
  max-width: 100%;
  min-height: 90px;
  border: 1px solid #7890a5;
  padding: 1rem;
}

/* ========== C90: RESPONSIVE LAYOUT ==========
   This rule applies only at 700px or narrower. Source order matters. */
@media (max-width: 700px) {
  h1 {
    font-size: 2.2rem;
  }

  .cards {
    grid-template-columns: 1fr;
  }

  .header-row {
    align-items: flex-start;
  }

  nav ul {
    gap: 0.8rem;
  }

}

/* ========== C91: PRINT ==========
   Print removes navigation and dark backgrounds to save ink. */
@media print {
  .site-header, .site-footer, .skip-link, button {
    display: none;
  }

  body {
    color: black;
    background: white;
  }

  .container {
    width: 100%;
  }

  a {
    color: black;
  }

}

/* ========== C22: SMALL PROPERTY COMPARISONS ==========
   These supplement the earlier examples; each selector matches an existing element. */
.transform-tile:active {
  transform: matrix(1, 0.1, 0, 1, 0, 0);
}

.circle-photo {
  margin-inline: auto;
}

.float-demo img {
  shape-outside: circle(50%);
  border-radius: 50%;
}

.selector-demo p::first-line {
  letter-spacing: 0.025em;
}

.selector-demo a:visited {
  color: #663399;
}

.selector-demo a:active {
  color: #a93917;
}

/* ========== C23: IMAGE MASK SOURCES ========== */
.png-mask, .svg-mask {
  width: 300px;
  height: 200px;
  object-fit: cover;
}

.png-mask {
  mask-image: url('../assets/placeholder.png');
  mask-mode: luminance;
  mask-size: 100% 100%;
}

.svg-mask {
  mask-image: url('../assets/mask.svg');
  mask-size: 100% 100%;
  mask-repeat: no-repeat;
}