/* ---------------------------------------------------
   Explain My Mistake — design tokens
   Palette: warm exam-paper cream + red-pen correction
--------------------------------------------------- */
:root{
  --paper: #FAF3E7;
  --paper-deep: #F1E8D8;
  --rule: #E1D3B8;
  --ink: #201D1A;
  --ink-soft: #56504A;
  --graphite: #7A7268;
  --red: #C1392B;
  --red-deep: #98291E;
  --green: #3F7D5C;
  --green-deep: #2E5F45;
  --highlight: #F2C14E;

  --font-display: "Fraunces", serif;
  --font-body: "Inter", -apple-system, BlinkMacSystemFont, sans-serif;
  --font-hand: "Kalam", cursive;

  --max: 1080px;
  --radius: 14px;
}

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

html{ scroll-behavior: smooth; }

body{
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--font-body);
  line-height: 1.55;
  -webkit-font-smoothing: antialiased;
  overflow-x: hidden;
  background-image:
    linear-gradient(var(--paper) 0%, var(--paper) 100%),
    repeating-linear-gradient(
      to bottom,
      transparent 0px, transparent 38px,
      var(--rule) 39px, transparent 40px
    );
  background-attachment: fixed;
}

.grain{
  position: fixed;
  inset: 0;
  z-index: 0;
  pointer-events: none;
  opacity: 0.035;
  mix-blend-mode: multiply;
  background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='160' height='160'%3E%3Cfilter id='n'%3E%3CfeTurbulence type='fractalNoise' baseFrequency='0.9' numOctaves='2' stitchTiles='stitch'/%3E%3C/filter%3E%3Crect width='100%25' height='100%25' filter='url(%23n)'/%3E%3C/svg%3E");
}

img, svg{ display: block; max-width: 100%; }
a{ color: inherit; }

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

:focus-visible{
  outline: 2.5px solid var(--red);
  outline-offset: 3px;
  border-radius: 4px;
}

button{ font: inherit; }

/* ---------------------------------------------------
   Header
--------------------------------------------------- */
.site-header{
  position: sticky;
  top: 0;
  z-index: 30;
  background: rgba(250, 243, 231, 0.86);
  backdrop-filter: blur(8px);
  border-bottom: 1.5px solid var(--rule);
}

.header-inner{
  max-width: var(--max);
  margin: 0 auto;
  padding: 16px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
}

.logo{
  display: flex; align-items: center; gap: 10px;
  text-decoration: none; color: var(--ink);
  font-family: var(--font-display); font-weight: 600;
  font-size: 1.05rem; letter-spacing: -0.01em;
}

.logo-mark{ width: 26px; height: 26px; color: var(--red); flex-shrink: 0; }

.nav{
  display: flex; gap: 28px;
  font-size: 0.95rem; font-weight: 500;
}

.nav a{
  text-decoration: none; color: var(--ink-soft);
  white-space: nowrap; position: relative;
  padding-bottom: 2px; transition: color 0.15s ease;
}
.nav a:hover{ color: var(--red); }
.nav a::after{
  content: ""; position: absolute; left: 0; right: 0; bottom: -3px;
  height: 2px; background: var(--red);
  transform: scaleX(0); transform-origin: left;
  transition: transform 0.2s ease;
}
.nav a:hover::after{ transform: scaleX(1); }

.nav-toggle{
  display: none;
  background: none; border: 1.5px solid var(--rule);
  border-radius: 8px; width: 42px; height: 38px;
  align-items: center; justify-content: center;
  color: var(--ink); cursor: pointer;
}
.nav-toggle svg{ width: 20px; height: 20px; }

/* ---------------------------------------------------
   Shared section rhythm
--------------------------------------------------- */
main{ position: relative; z-index: 1; max-width: var(--max); margin: 0 auto; padding: 0 24px; }

section{ padding: clamp(56px, 9vw, 96px) 0; }

.eyebrow{
  font-family: var(--font-hand); color: var(--red);
  font-size: 1.15rem; margin: 0 0 6px;
  transform: rotate(-1.2deg);
}
.eyebrow.center{ text-align: center; }

.section-title{
  font-family: var(--font-display); font-weight: 600;
  font-size: clamp(1.6rem, 3vw, 2.2rem);
  letter-spacing: -0.01em; margin: 0 0 18px;
}
.section-title.center{ text-align: center; }

/* ---------------------------------------------------
   Hero + Tool
--------------------------------------------------- */
.hero{
  display: grid;
  grid-template-columns: 1.05fr 1fr;
  gap: clamp(32px, 5vw, 56px);
  align-items: start;
  padding-top: clamp(40px, 8vw, 72px);
}

.hero-copy h1{
  font-family: var(--font-display); font-weight: 600;
  font-size: clamp(2.1rem, 5vw, 3.6rem);
  line-height: 1.08; letter-spacing: -0.02em;
  margin: 0 0 22px;
}

.underline-wrap{ position: relative; display: inline-block; }
.underline-svg{
  position: absolute; left: 0; bottom: -10px;
  width: 100%; height: 16px; overflow: visible;
}
.underline-path{
  stroke-dasharray: 400; stroke-dashoffset: 400;
  animation: draw 1.1s 0.5s cubic-bezier(.4,.7,.3,1) forwards;
}
@keyframes draw{ to{ stroke-dashoffset: 0; } }

.hero-sub{ color: var(--ink-soft); font-size: clamp(1rem, 1.6vw, 1.08rem); max-width: 44ch; }

.hero-meta{
  display: flex; align-items: center; gap: 10px;
  margin-top: 24px; font-size: 0.86rem; color: var(--graphite);
}
.hero-meta .dot{ width: 6px; height: 6px; border-radius: 50%; background: var(--green); flex-shrink: 0; }

/* Tool card styled like a page of graded exam paper */
.tool-card{
  position: relative;
  background: #fff;
  border-radius: var(--radius);
  padding: 32px 28px 28px;
  box-shadow: 0 18px 40px -14px rgba(32,29,26,0.22), 0 2px 0 rgba(32,29,26,0.03);
  border: 1px solid var(--rule);
}

.tool-tape{
  position: absolute; top: -14px; left: 32px;
  width: 90px; height: 26px;
  background: rgba(242,193,78,0.55);
  transform: rotate(-3deg); border-radius: 2px;
}

.field{ margin-bottom: 16px; }

.field-head{ display: flex; align-items: baseline; justify-content: space-between; margin-bottom: 6px; }

.field label{
  display: block; font-size: 0.82rem; font-weight: 600;
  text-transform: uppercase; letter-spacing: 0.06em;
  color: var(--graphite);
}

textarea, input[type="text"]{
  width: 100%;
  font-family: var(--font-body); font-size: 1rem; color: var(--ink);
  padding: 12px 14px; border: 1.5px solid var(--rule);
  border-radius: 8px; background: var(--paper);
  resize: vertical;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

textarea:focus, input[type="text"]:focus{
  border-color: var(--red);
  box-shadow: 0 0 0 3px rgba(193,57,43,0.12);
  outline: none;
}

#go{
  width: 100%;
  display: inline-flex; align-items: center; justify-content: center; gap: 10px;
  background: var(--red); color: #fff; border: none;
  padding: 14px 20px; font-weight: 600; font-size: clamp(0.95rem, 2vw, 1.02rem);
  border-radius: 8px; cursor: pointer;
  transition: transform 0.15s ease, background 0.15s ease, box-shadow 0.15s ease, opacity 0.15s ease;
  box-shadow: 0 8px 18px -8px rgba(193,57,43,0.55);
}
#go:hover:not(:disabled){ background: var(--red-deep); transform: translateY(-1px); }
#go:active:not(:disabled){ transform: translateY(0); }
#go:disabled{ opacity: 0.75; cursor: progress; }
.pen-icon{ width: 18px; height: 18px; flex-shrink: 0; }
.pen-icon.spin{ animation: nudge 0.9s ease-in-out infinite; }
@keyframes nudge{ 0%,100%{ transform: rotate(0deg); } 50%{ transform: rotate(-14deg) translateY(-1px); } }

.hint{ margin: 10px 0 0; font-size: 0.8rem; color: var(--graphite); text-align: center; }
.hint kbd{
  font-family: var(--font-body); font-size: 0.75rem;
  border: 1px solid var(--rule); border-bottom-width: 2px;
  border-radius: 4px; padding: 1px 5px; background: var(--paper-deep);
}

/* ---------------------------------------------------
   Output / "graded paper" result
--------------------------------------------------- */
.out{ margin-top: 6px; }
.out:empty{ margin-top: 0; }

.grade-wrap{
  margin-top: 26px; padding-top: 22px;
  border-top: 2px dashed var(--rule);
  animation: rise 0.45s ease both;
}
@keyframes rise{ from{ opacity: 0; transform: translateY(8px); } to{ opacity: 1; transform: translateY(0); } }

.grade-head{ display: flex; align-items: center; gap: 14px; margin-bottom: 18px; }

.grade-mark{ width: 46px; height: 46px; color: var(--red); flex-shrink: 0; }
.grade-wrap.is-correct .grade-mark{ color: var(--green); }
.grade-mark circle, .grade-mark path{
  stroke-dasharray: 140; stroke-dashoffset: 140;
  animation: circle-in 0.6s 0.1s ease forwards;
}
@keyframes circle-in{ to{ stroke-dashoffset: 0; } }

.grade-note{
  font-family: var(--font-hand); color: var(--red-deep);
  font-size: 1.25rem; transform: rotate(-1deg);
}
.grade-wrap.is-correct .grade-note{ color: var(--green-deep); }

.grade-block{ padding: 14px 0; border-bottom: 1px solid var(--rule); }
.grade-block:last-child{ border-bottom: none; padding-bottom: 0; }

.grade-block h4{
  margin: 0 0 6px; font-size: 0.78rem; text-transform: uppercase;
  letter-spacing: 0.06em; color: var(--graphite); font-weight: 700;
}
.grade-block p{ margin: 0; color: var(--ink); }
.grade-block code{
  font-family: ui-monospace, "SF Mono", Consolas, monospace;
  background: var(--paper-deep); border: 1px solid var(--rule);
  border-radius: 4px; padding: 1px 5px; font-size: 0.92em;
}

.grade-block.highlight{
  background: linear-gradient(90deg, rgba(242,193,78,0.18), transparent);
  padding-left: 12px; margin-left: -12px; border-radius: 6px;
}
.grade-wrap.is-correct .grade-block.highlight{
  background: linear-gradient(90deg, rgba(63,125,92,0.14), transparent);
}

.out.warning{
  color: var(--red-deep); font-family: var(--font-hand);
  font-size: 1.15rem; margin-top: 14px;
}

.skeleton{ margin-top: 26px; padding-top: 22px; border-top: 2px dashed var(--rule); }
.skeleton-line{
  height: 14px; border-radius: 6px; margin-bottom: 12px;
  background: linear-gradient(90deg, var(--paper-deep) 25%, var(--rule) 37%, var(--paper-deep) 63%);
  background-size: 400% 100%; animation: shimmer 1.4s ease infinite;
}
@keyframes shimmer{ 0%{ background-position: 100% 0; } 100%{ background-position: -100% 0; } }

/* ---------------------------------------------------
   How it works
--------------------------------------------------- */
.steps{
  list-style: none; margin: 44px 0 0; padding: 0;
  display: grid; grid-template-columns: repeat(3, 1fr); gap: 28px;
}

.steps li{
  background: #fff; border: 1px solid var(--rule);
  border-radius: var(--radius); padding: 26px 24px 24px;
  position: relative; transition: transform 0.2s ease, box-shadow 0.2s ease;
}
.steps li:hover{
  transform: translateY(-4px);
  box-shadow: 0 16px 30px -18px rgba(32,29,26,0.28);
}

.steps .num{
  display: block; font-family: var(--font-display); font-weight: 600;
  font-size: 1.6rem; color: var(--red); opacity: 0.85; margin-bottom: 10px;
}
.steps h3{ font-family: var(--font-display); font-size: 1.2rem; margin: 0 0 8px; }
.steps p{ margin: 0; color: var(--ink-soft); font-size: 0.97rem; }

/* ---------------------------------------------------
   About
--------------------------------------------------- */
.about-grid{
  display: grid; grid-template-columns: 1.3fr 1fr;
  gap: 48px; align-items: center;
}

.about-text p{ color: var(--ink-soft); font-size: 1.03rem; }
.about-text em{ color: var(--ink); font-style: italic; }

.about-note{
  background: var(--paper-deep); border: 1px solid var(--rule);
  border-radius: var(--radius); padding: 32px 28px;
  transform: rotate(1deg);
}
.about-note .hand{
  font-family: var(--font-hand); font-size: clamp(1.2rem, 2.4vw, 1.5rem);
  line-height: 1.4; color: var(--red-deep); margin: 0;
}

/* ---------------------------------------------------
   Footer
--------------------------------------------------- */
.site-footer{
  position: relative; z-index: 1;
  border-top: 1.5px solid var(--rule);
  background: var(--paper-deep);
  padding: 40px 24px 32px;
}
.footer-inner{ max-width: var(--max); margin: 0 auto; text-align: center; color: var(--graphite); }
.footer-inner .logo{ justify-content: center; margin-bottom: 10px; }
.footer-inner p{ margin: 0 0 6px; font-size: 0.95rem; }
.footer-inner small{ font-size: 0.82rem; }

/* ---------------------------------------------------
   Scroll reveal
--------------------------------------------------- */
.reveal{
  opacity: 0; transform: translateY(16px);
  transition: opacity 0.6s ease, transform 0.6s ease;
}
.reveal.in-view{ opacity: 1; transform: translateY(0); }

@media (prefers-reduced-motion: reduce){
  .reveal{ opacity: 1; transform: none; transition: none; }
  .underline-path{ animation: none; stroke-dashoffset: 0; }
  .grade-mark circle, .grade-mark path{ animation: none; stroke-dashoffset: 0; }
  .pen-icon.spin{ animation: none; }
  .skeleton-line{ animation: none; }
  html{ scroll-behavior: auto; }
}

/* ---------------------------------------------------
   Responsive
--------------------------------------------------- */
@media (max-width: 900px){
  .hero{ grid-template-columns: 1fr; gap: 36px; padding-top: 40px; }
  .steps{ grid-template-columns: 1fr; }
  .about-grid{ grid-template-columns: 1fr; }
  .about-note{ transform: none; }
}

@media (max-width: 640px){
  .nav{
    position: fixed; top: 68px; left: 16px; right: 16px;
    background: var(--paper); border: 1px solid var(--rule);
    border-radius: 12px; padding: 10px; flex-direction: column; gap: 2px;
    box-shadow: 0 18px 30px -12px rgba(32,29,26,0.2);
    transform: translateY(-8px) scale(0.98); opacity: 0; visibility: hidden;
    transition: transform 0.18s ease, opacity 0.18s ease, visibility 0.18s;
  }
  .nav.is-open{ transform: translateY(0) scale(1); opacity: 1; visibility: visible; }
  .nav a{ padding: 10px 10px; border-radius: 8px; }
  .nav a:hover{ background: var(--paper-deep); }
  .nav a::after{ display: none; }
  .nav-toggle{ display: inline-flex; }
}

@media (max-width: 560px){
  .tool-card{ padding: 24px 18px 20px; }
  .logo span{ font-size: 0.95rem; }
}