:root {
  --ink: #17212b;
  --muted: #687582;
  --line: #e6ebef;
  --paper: #f7f9fb;
  --card: #ffffff;
  --blue: #2b67f6;
  --blue-dark: #1e4fc7;
  --blue-soft: #edf3ff;
  --green: #16845b;
  --amber: #a46b13;
  --shadow: 0 18px 50px rgba(29, 49, 72, .07);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--ink);
  background: var(--paper);
}
* { box-sizing: border-box; }
body { margin: 0; min-width: 320px; background: var(--paper); }
button, textarea { font: inherit; }
.site-header { height: 76px; display: flex; align-items: center; justify-content: space-between; max-width: 1240px; margin: auto; padding: 0 32px; border-bottom: 1px solid var(--line); }
.brand { display: flex; align-items: center; gap: 10px; color: var(--ink); text-decoration: none; font-size: 15px; font-weight: 750; letter-spacing: .05em; }
.brand em { color: var(--muted); font-style: normal; font-weight: 500; }
.brand-mark { display: grid; place-items: center; width: 29px; height: 29px; border-radius: 8px; color: white; background: var(--blue); font-size: 15px; letter-spacing: 0; }
.header-note { color: var(--muted); font-size: 12px; letter-spacing: .02em; }
.shell { max-width: 1240px; margin: auto; padding: 72px 32px 52px; }
.hero { max-width: 730px; margin-bottom: 45px; }
.eyebrow, .card-kicker { color: var(--blue); font-size: 11px; font-weight: 750; letter-spacing: .14em; }
.hero h1 { margin: 15px 0 17px; font-size: clamp(36px, 5vw, 62px); line-height: 1.04; letter-spacing: -.055em; font-weight: 780; }
.hero h1 span { color: var(--blue); }
.lede { max-width: 620px; margin: 0; color: var(--muted); font-size: 16px; line-height: 1.7; }
.workspace { display: grid; grid-template-columns: minmax(290px, .78fr) minmax(420px, 1.22fr); align-items: start; gap: 24px; }
.exercise-card, .trace-card { background: var(--card); border: 1px solid var(--line); border-radius: 16px; box-shadow: var(--shadow); }
.exercise-card { padding: 27px; }
.status-dot { display: inline-block; width: 7px; height: 7px; margin-right: 7px; border-radius: 50%; background: var(--green); vertical-align: 1px; }
.exercise-card label { display: block; margin: 30px 0 11px; color: var(--ink); font-size: 14px; font-weight: 700; }
textarea { display: block; width: 100%; min-height: 210px; resize: vertical; padding: 15px; color: var(--ink); background: #fbfcfd; border: 1px solid var(--line); border-radius: 10px; outline: none; font-size: 14px; line-height: 1.6; transition: border-color .2s, box-shadow .2s; }
textarea:focus { border-color: var(--blue); box-shadow: 0 0 0 4px rgba(43,103,246,.1); }
.form-meta { display: flex; justify-content: space-between; gap: 10px; margin: 9px 1px 20px; color: var(--muted); font-size: 11px; }
.primary-button { display: flex; width: 100%; justify-content: space-between; align-items: center; padding: 14px 16px; color: white; background: var(--blue); border: 0; border-radius: 9px; cursor: pointer; font-size: 13px; font-weight: 700; transition: background .2s, transform .2s; }
.primary-button:hover { background: var(--blue-dark); transform: translateY(-1px); }
.primary-button:disabled { cursor: not-allowed; color: #667485; background: #dce3ea; opacity: 1; transform: none; }
.button-arrow { font-size: 19px; line-height: 12px; }
.privacy-note { margin: 18px 0 0; color: var(--muted); font-size: 11px; line-height: 1.55; }
.trace-card { min-height: 0; overflow: hidden; }
.trace-head { display: flex; justify-content: space-between; align-items: flex-start; padding: 27px 28px 23px; border-bottom: 1px solid var(--line); }
.trace-head h2 { margin: 8px 0 0; font-size: 22px; letter-spacing: -.03em; }
.run-status { padding: 6px 9px; border-radius: 999px; color: var(--muted); background: #f2f4f6; font-size: 11px; font-weight: 700; }
.run-status.running { color: var(--blue); background: var(--blue-soft); }
.run-status.done { color: var(--green); background: #eaf8f1; }
.run-status.error { color: #a53838; background: #fff0f0; }
.trace-empty { padding: 84px 35px; text-align: center; color: var(--muted); }
.empty-icon { display: grid; place-items: center; width: 48px; height: 48px; margin: 0 auto 18px; border: 1px solid #cddcff; border-radius: 14px; color: var(--blue); background: var(--blue-soft); font-size: 21px; }
.trace-empty h3 { margin: 0 0 8px; color: var(--ink); font-size: 15px; }
.trace-empty p { max-width: 310px; margin: auto; font-size: 12px; line-height: 1.6; }
.trace-list { padding: 8px 28px 20px; }
.trace-step { position: relative; display: grid; grid-template-columns: 28px 1fr; gap: 13px; padding: 18px 0 18px; border-bottom: 1px solid var(--line); animation: rise .3s ease both; }
.trace-step:last-child { border-bottom: 0; }
.step-rail { position: relative; display: flex; justify-content: center; }
.step-rail::after { content: ""; position: absolute; top: 22px; bottom: -37px; width: 1px; background: #dce5f5; }
.trace-step:last-child .step-rail::after { display: none; }
.step-marker { z-index: 1; display: grid; place-items: center; width: 25px; height: 25px; border: 1px solid #cbd9fb; border-radius: 50%; color: var(--blue); background: white; font-size: 10px; font-weight: 800; }
.trace-step.active .step-marker { color: white; background: var(--blue); border-color: var(--blue); box-shadow: 0 0 0 4px #e9efff; }
.step-title { margin: 1px 0 5px; color: var(--ink); font-size: 13px; font-weight: 750; }
.step-status { margin-left: 7px; color: var(--muted); font-size: 10px; font-weight: 500; }
.step-body { color: var(--muted); font-size: 12px; line-height: 1.65; white-space: pre-wrap; overflow-wrap: anywhere; }
.step-body strong { color: var(--ink); }
.step-error { color: #a53838; }
.final-answer { margin: 3px 28px 28px; padding: 18px; border: 1px solid #cde9dc; border-radius: 11px; background: #f2fbf6; }
.final-answer .card-kicker { color: var(--green); }
.final-answer-text { margin-top: 8px; color: var(--ink); font-size: 14px; line-height: 1.7; white-space: pre-wrap; overflow-wrap: anywhere; }
.principles { display: grid; grid-template-columns: repeat(3, 1fr); gap: 24px; margin-top: 65px; padding-top: 25px; border-top: 1px solid var(--line); }
.principles > div { display: grid; grid-template-columns: 35px 1fr; column-gap: 11px; }
.principle-icon { grid-row: span 2; color: var(--blue); font-size: 11px; font-weight: 800; padding-top: 2px; }
.principles strong { font-size: 13px; }
.principles p { margin: 5px 0 0; color: var(--muted); font-size: 12px; line-height: 1.55; }
.disclaimer { margin: 38px 0 0; color: #8b969e; text-align: center; font-size: 11px; }
@keyframes rise { from { opacity: 0; transform: translateY(5px); } to { opacity: 1; transform: translateY(0); } }
@media (max-width: 780px) { .site-header { height: 66px; padding: 0 18px; } .header-note { display: none; } .shell { padding: 48px 18px 35px; } .hero { margin-bottom: 30px; } .workspace { grid-template-columns: 1fr; } .trace-card { min-height: 400px; } .trace-empty { padding: 70px 25px; } .principles { grid-template-columns: 1fr; gap: 18px; margin-top: 40px; } }
@media (max-width: 430px) { .hero h1 { font-size: 38px; } .lede { font-size: 14px; } .exercise-card { padding: 21px; } .trace-head { padding: 22px 20px 19px; } .trace-list { padding-left: 20px; padding-right: 20px; } .final-answer { margin-left: 20px; margin-right: 20px; } .form-meta { font-size: 10px; } }