/* ---------------------------------------------------------------- 토큰 */
:root {
  --bg: #eef2f7;
  --grid: rgba(23, 42, 69, .055);
  --panel: rgba(255, 255, 255, .82);
  --panel-solid: #ffffff;
  --panel-2: rgba(255, 255, 255, .55);
  --line: rgba(23, 42, 69, .12);
  --line-soft: rgba(23, 42, 69, .07);
  --ink: #16202e;
  --ink-2: #4a5768;
  --ink-3: #868f9f;
  --accent: #3b82c4;
  --accent-soft: rgba(59, 130, 196, .1);
  --ok: #17916a;
  --ok-soft: rgba(23, 145, 106, .11);
  --warn: #b8781f;
  --warn-soft: rgba(184, 120, 31, .12);
  --bad: #cf4257;
  --bad-soft: rgba(207, 66, 87, .11);

  --lv-easy: #34a877;
  --lv-medium: #d99a2b;
  --lv-hard: #de5f74;
  --lv-monster: #8e6fd8;
  --lv-practice: #3b82c4;
  --lv-archive: #5b93c9;
  --lv-stats: #6b7a90;

  /* 종이 위에 얹힌 듯한 아주 옅은 그림자 — 이 디자인의 기본 질감 */
  --lift: 0 1px 1px rgba(23, 42, 69, .04), 0 6px 18px rgba(23, 42, 69, .07);
  --lift-lg: 0 2px 4px rgba(23, 42, 69, .05), 0 18px 44px rgba(23, 42, 69, .10);
  --radius: 18px;
  --serif: "KaTeX_Main", Georgia, "Times New Roman", serif;
  --mono: ui-monospace, SFMono-Regular, "SF Mono", Menlo, Consolas, monospace;
}

html[data-theme="dark"] {
  --bg: #0e1319;
  --grid: rgba(150, 180, 220, .05);
  --panel: rgba(28, 35, 45, .78);
  --panel-solid: #1a212a;
  --panel-2: rgba(255, 255, 255, .04);
  --line: rgba(160, 190, 225, .14);
  --line-soft: rgba(160, 190, 225, .08);
  --ink: #e9eef5;
  --ink-2: #a9b4c4;
  --ink-3: #78849a;
  --accent: #6fa8dc;
  --accent-soft: rgba(111, 168, 220, .13);
  --ok: #4cc794;
  --ok-soft: rgba(76, 199, 148, .12);
  --warn: #e0aa5a;
  --warn-soft: rgba(224, 170, 90, .13);
  --bad: #ef7f92;
  --bad-soft: rgba(239, 127, 146, .13);

  --lv-easy: #4cc794;
  --lv-medium: #e0aa5a;
  --lv-hard: #ef7f92;
  --lv-monster: #ab8ff0;
  --lv-practice: #6fa8dc;
  --lv-archive: #7fb3e0;
  --lv-stats: #94a2b8;

  --lift: 0 1px 1px rgba(0, 0, 0, .3), 0 8px 24px rgba(0, 0, 0, .34);
  --lift-lg: 0 2px 6px rgba(0, 0, 0, .35), 0 22px 52px rgba(0, 0, 0, .45);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  color: var(--ink);
  font-family: "Pretendard", -apple-system, BlinkMacSystemFont, "Segoe UI",
    "Apple SD Gothic Neo", "Noto Sans KR", Roboto, sans-serif;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;

  /* 모눈종이 바탕 */
  background-color: var(--bg);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 72px 72px;
  background-position: center top;
}

/* 세로로만 움직인다. 무엇 하나가 조금 삐져나가더라도 화면이 옆으로 끌려가지 않게. */
html, body { overflow-x: hidden; overscroll-behavior-x: none; }
body { max-width: 100%; }

button { font: inherit; color: inherit; cursor: pointer; }
input { font: inherit; }

/* 작은 안내 글씨는 전부 자간 넓힌 대문자로 — 이 사이트의 표지 글꼴 규칙 */
.kicker, .eyebrow, .orb .lab, .backwrap .lab, .preview .label, .solution h3, .stat .k {
  text-transform: uppercase;
  letter-spacing: .16em;
  font-size: 11px;
  font-weight: 500;
  color: var(--ink-3);
}

/* ---------------------------------------------------------------- 레이아웃 */
.wrap { max-width: 900px; margin: 0 auto; padding: 18px 16px 72px; }

header.top {
  display: flex; align-items: center; gap: 10px; flex-wrap: nowrap;
  padding: 8px 0 20px;
}
.brand { display: flex; align-items: center; gap: 11px; margin-right: auto; }
.brand .sym {
  width: 42px; height: 42px; flex: 0 0 42px;
  border-radius: 999px; border: 1px solid var(--line); background: var(--panel);
  box-shadow: var(--lift); display: grid; place-items: center;
  font-family: var(--serif); font-size: 24px; line-height: 1; color: var(--accent);
  backdrop-filter: blur(6px);
}
.brand h1 { font-family: var(--serif); font-size: 21px; margin: 0; font-weight: 700; letter-spacing: -.01em; }
.brand .tag { font-size: 11.5px; color: var(--ink-3); letter-spacing: .04em; }
/* 허브에서는 가운데 표제가 곧 로고이므로 헤더의 브랜드를 접는다 */
body[data-view="hub"] .brand { display: none; }
body[data-view="hub"] header.top { justify-content: flex-end; }

.pill {
  display: inline-flex; align-items: center; gap: 7px;
  background: var(--panel); border: 1px solid var(--line);
  border-radius: 999px; padding: 7px 14px; font-size: 12.5px; color: var(--ink-2);
  box-shadow: var(--lift); backdrop-filter: blur(6px);
}
.pill b { color: var(--ink); font-variant-numeric: tabular-nums; font-family: var(--serif); }
.pill.flame b { color: var(--warn); }

.icon-btn {
  width: 40px; height: 40px; border-radius: 999px;
  border: 1px solid var(--line); background: var(--panel);
  display: grid; place-items: center; box-shadow: var(--lift);
  backdrop-filter: blur(6px); transition: border-color .15s, transform .15s;
}
.icon-btn:hover { border-color: var(--accent); transform: translateY(-1px); }

/* ---------------------------------------------------------------- 구슬 허브 */
#hubView { display: grid; place-items: center; min-height: min(66vh, 520px); }

.hub {
  position: relative;
  width: 100%; max-width: var(--hub-max, 470px); margin: 8px auto 0;
  aspect-ratio: 1 / 1;

  /* 반지름과 구슬 크기를 상자 폭에 비례시킨다.
     예전에는 px 로 못 박아 둬서, 화면이 좁으면 고리가 상자보다 커지고
     구슬이 밖으로 삐져나가 페이지가 가로로 밀렸다.
     .366 은 hub-web(viewBox 100×100)의 WEB_R = 36.5 와 맞춘 값이다. */
  --hub-max: 470px;
  --hub-w: min(calc(100vw - 34px), var(--hub-max));
  --r: calc(var(--hub-w) * .366);
  --orb: calc(var(--hub-w) * .166);
}
/* 구슬과 점선 웹을 담는 고리. 평소엔 멈춰 있다가 구슬을 누르면
   그 구슬이 맨 위로 오도록 돈다. 회전각은 JS 가 인라인 transform 으로 넣는다.
   구슬 안쪽 .spin 이 같은 각을 반대로 되감아 글자·라벨은 늘 똑바로 선다. */
.hub-ring {
  position: absolute; inset: 0;
  transition: transform var(--turn, .62s) cubic-bezier(.22, .61, .36, 1);
}
.orb .spin {
  position: relative; display: block; width: 100%; height: 100%;
  transition: transform var(--turn, .62s) cubic-bezier(.22, .61, .36, 1);
}

/* 맨 위에 올라온 구슬을 살짝 강조한다 */
.orb.top .ball {
  box-shadow: var(--lift-lg), 0 0 0 12px color-mix(in srgb, var(--c) 11%, transparent);
  border-color: color-mix(in srgb, var(--c) 62%, transparent);
}

.hub-web { position: absolute; inset: 0; width: 100%; height: 100%; overflow: visible; }
.hub-web line, .hub-web polygon {
  fill: none; stroke: var(--line); stroke-width: 1;
  stroke-dasharray: 2 7; stroke-linecap: round;
  vector-effect: non-scaling-stroke;
}
.hub-web line { opacity: .45; }

.hub-core {
  position: absolute; left: 50%; top: 50%; z-index: 1; transform: translate(-50%, -50%);
  text-align: center; width: 56%; pointer-events: none;
}
.hub-core .word {
  font-family: var(--serif); font-weight: 700;
  font-size: clamp(26px, 7.6vw, 42px); line-height: 1.05;
  color: var(--accent); letter-spacing: -.015em;
}
.hub-core .kicker { font-style: italic; text-transform: none; letter-spacing: .02em; font-size: 15px; color: var(--ink-2); font-family: var(--serif); }

.orb {
  position: absolute; left: 50%; top: 50%;
  width: var(--orb); height: var(--orb);
  margin-left: calc(var(--orb) / -2); margin-top: calc(var(--orb) / -2);
  transform: rotate(var(--a)) translate(var(--r)) rotate(calc(-1 * var(--a)));
  border: 0; padding: 0; background: none;
}
.orb .ball {
  width: 100%; height: 100%; border-radius: 999px;
  display: grid; place-items: center;
  font-family: var(--serif); font-size: 25px; font-weight: 700;
  color: var(--c); border: 1px solid color-mix(in srgb, var(--c) 34%, transparent);
  background:
    radial-gradient(circle at 50% 42%, color-mix(in srgb, var(--c) 13%, transparent), transparent 72%),
    var(--panel);
  box-shadow: var(--lift), 0 0 0 8px color-mix(in srgb, var(--c) 7%, transparent);
  backdrop-filter: blur(4px);
  transition: transform .18s ease, box-shadow .18s ease;
}
.orb .lab {
  position: absolute; left: 50%; top: calc(100% + 9px); transform: translateX(-50%);
  white-space: nowrap; color: var(--ink-2); font-size: 11.5px; letter-spacing: .1em;
}
.orb:hover .ball, .orb:focus-visible .ball {
  transform: translateY(-3px) scale(1.05);
  box-shadow: var(--lift-lg), 0 0 0 12px color-mix(in srgb, var(--c) 10%, transparent);
}
.orb .tick {
  position: absolute; right: 2px; top: 2px;
  width: 20px; height: 20px; border-radius: 999px;
  background: var(--panel-solid); color: var(--ok);
  border: 1px solid var(--line); box-shadow: var(--lift);
  font-size: 11px; display: grid; place-items: center;
}

/* 되돌아가기 구슬 */
.backwrap { display: none; flex-direction: column; align-items: center; gap: 7px; margin: 0 auto 20px; width: max-content; }
body:not([data-view="hub"]) .backwrap { display: flex; }
.orb-back {
  width: 52px; height: 52px; border-radius: 999px;
  border: 1px solid var(--line); background: var(--panel);
  box-shadow: var(--lift), 0 0 0 8px var(--panel-2);
  font-size: 19px; color: var(--ink-2); backdrop-filter: blur(6px);
  transition: transform .18s ease, border-color .15s;
}
.orb-back:hover { transform: translateY(-2px); border-color: var(--accent); color: var(--ink); }

/* ---------------------------------------------------------------- 난이도 바 */
.levels { display: flex; gap: 8px; margin-bottom: 18px; flex-wrap: wrap; justify-content: center; }
.levels button {
  border: 1px solid var(--line); background: var(--panel); border-radius: 999px;
  padding: 8px 17px; font-size: 13px; color: var(--ink-2);
  display: inline-flex; gap: 8px; align-items: center;
  box-shadow: var(--lift); backdrop-filter: blur(6px);
  letter-spacing: .04em; transition: transform .15s, border-color .15s;
}
.levels button:hover { transform: translateY(-1px); }
.levels button[aria-selected="true"] { color: var(--ink); font-weight: 600; }
.levels .dot { width: 8px; height: 8px; border-radius: 999px; background: var(--line); }
.levels .dot.easy { background: var(--lv-easy); }
.levels .dot.medium { background: var(--lv-medium); }
.levels .dot.hard { background: var(--lv-hard); }
.levels .dot.monster { background: var(--lv-monster); }
.levels button[data-level="easy"][aria-selected="true"] { border-color: var(--lv-easy); box-shadow: var(--lift), 0 0 0 4px color-mix(in srgb, var(--lv-easy) 12%, transparent); }
.levels button[data-level="medium"][aria-selected="true"] { border-color: var(--lv-medium); box-shadow: var(--lift), 0 0 0 4px color-mix(in srgb, var(--lv-medium) 12%, transparent); }
.levels button[data-level="hard"][aria-selected="true"] { border-color: var(--lv-hard); box-shadow: var(--lift), 0 0 0 4px color-mix(in srgb, var(--lv-hard) 12%, transparent); }
.levels button[data-level="monster"][aria-selected="true"] { border-color: var(--lv-monster); box-shadow: var(--lift), 0 0 0 4px color-mix(in srgb, var(--lv-monster) 12%, transparent); }
.levels .check { color: var(--ok); font-size: 12px; }

/* ------------------------------------------------------- 연습 모드 하루 몫 */
.quota {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  justify-content: center; margin: -6px 0 18px;
}
.quota-info { font-size: 12px; color: var(--ink-3); letter-spacing: .04em; }
.quota-info b { color: var(--ink-2); font-family: var(--serif); font-size: 13.5px; }
.quota-info i { font-style: normal; opacity: .45; margin: 0 7px; }

.levels .left {
  min-width: 18px; height: 18px; padding: 0 5px; border-radius: 999px;
  background: var(--panel-2); border: 1px solid var(--line-soft);
  font-family: var(--serif); font-size: 11px; color: var(--ink-3);
  display: inline-grid; place-items: center;
}
.levels .left.out { color: var(--bad); border-color: color-mix(in srgb, var(--bad) 35%, transparent); }

.card.lock { text-align: center; }
.card.lock .card-head { justify-content: center; }
.lock-msg { font-size: 15px; margin: 0 0 6px; color: var(--ink-2); }
.lock-msg b { color: var(--ink); }
.card.lock .muted { margin: 0 0 6px; }

/* Touch Grass — 한도에 부딪히면 나오는 잔디밭 */
.grass {
  position: relative; overflow: hidden;
  margin: 16px 0 18px; border-radius: 14px;
  aspect-ratio: 20 / 9; min-height: 150px;
  border: 1px solid var(--line-soft);
  box-shadow: inset 0 0 0 1px rgba(255, 255, 255, .18);
  display: grid; place-items: center;
}
.grass-svg, .grass-photo {
  position: absolute; inset: 0; width: 100%; height: 100%;
  object-fit: cover; display: block;
}
.grass-photo { z-index: 1; }
.grass-cap {
  position: relative; z-index: 2;
  font-family: var(--serif); font-weight: 700;
  font-size: clamp(30px, 8vw, 52px); line-height: 1;
  color: #fff; letter-spacing: -.01em;
  text-shadow: 0 2px 3px rgba(20, 45, 15, .45), 0 10px 30px rgba(20, 45, 15, .5);
}

/* ---------------------------------------------------------------- 카드 */
.card {
  background: var(--panel); border: 1px solid var(--line);
  border-radius: var(--radius); box-shadow: var(--lift);
  backdrop-filter: blur(10px);
  padding: 24px; margin-bottom: 16px;
}
.card-head { display: flex; align-items: center; gap: 10px; margin-bottom: 4px; flex-wrap: wrap; }
.chip {
  font-size: 10.5px; padding: 4px 12px; border-radius: 999px;
  background: var(--panel-2); color: var(--ink-3); border: 1px solid var(--line-soft);
  text-transform: uppercase; letter-spacing: .13em;
}
.chip.mode { background: var(--warn-soft); color: var(--warn); border-color: transparent; }
.card-head .spacer { margin-left: auto; }

.problem {
  display: grid; place-items: center; min-height: 128px;
  padding: 22px 8px; margin: 14px 0 6px;
  background:
    linear-gradient(var(--grid) 1px, transparent 1px) center / 24px 24px,
    linear-gradient(90deg, var(--grid) 1px, transparent 1px) center / 24px 24px,
    var(--panel-2);
  border: 1px solid var(--line-soft); border-radius: 14px;
  font-size: 32px; overflow-x: auto;
}
.problem .fallback { font-family: var(--mono); font-size: 17px; color: var(--ink); }

/* ---------------------------------------------------------------- 입력 */
.answer-row { display: flex; gap: 8px; margin-top: 16px; flex-wrap: wrap; }
.answer-row input {
  flex: 1 1 260px; min-width: 0;
  padding: 13px 18px; border-radius: 999px;
  border: 1px solid var(--line); background: var(--panel-solid); color: var(--ink);
  box-shadow: var(--lift);
  font-family: var(--serif);
  font-size: 19px; letter-spacing: .01em;
}
.answer-row input::placeholder { font-size: 14px; opacity: .6; letter-spacing: 0; }
.answer-row input:focus { outline: 0; border-color: var(--accent); box-shadow: var(--lift), 0 0 0 4px var(--accent-soft); }

.btn {
  border: 1px solid var(--accent); border-radius: 999px; padding: 13px 24px;
  background: var(--accent); color: #fff; font-weight: 600; font-size: 14px;
  letter-spacing: .04em; box-shadow: var(--lift);
  transition: transform .15s, filter .15s;
}
.btn:hover { filter: brightness(1.07); transform: translateY(-1px); }
.btn:disabled { opacity: .5; cursor: not-allowed; filter: none; transform: none; }
.btn.ghost { background: var(--panel); color: var(--ink-2); border-color: var(--line); font-weight: 500; backdrop-filter: blur(6px); }
.btn.ghost:hover { border-color: var(--accent); color: var(--ink); filter: none; }
.btn.sm { padding: 9px 16px; font-size: 12px; }

.preview {
  margin-top: 14px; min-height: 64px; padding: 12px 18px;
  border-radius: 14px; background: var(--panel-2); color: var(--ink);
  border: 1px solid var(--line-soft);
  font-size: 22px; display: flex; align-items: center; gap: 16px; overflow-x: auto;
}
.preview .label { flex: 0 0 auto; align-self: center; }
.preview .muted { font-size: 13px; }
.preview.empty { background: transparent; border-style: dashed; }
.preview.err { color: var(--bad); font-size: 13px; }

.palette { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 12px; }
.palette button {
  border: 1px solid var(--line-soft); background: var(--panel-2); color: var(--ink-2);
  border-radius: 999px; padding: 6px 14px; font-size: 14px;
  font-family: var(--serif); transition: border-color .15s, transform .15s;
}
.palette button:hover { border-color: var(--accent); color: var(--ink); transform: translateY(-1px); }
/* 정적분 문항에서는 적분상수 버튼이 의미가 없다 */
.palette.def button:last-child { display: none; }

.actions { display: flex; gap: 8px; margin-top: 16px; flex-wrap: wrap; }
.actions .spacer { margin-left: auto; }

/* ---------------------------------------------------------------- 피드백 */
.feedback { margin-top: 16px; padding: 14px 18px; border-radius: 14px; font-size: 14px; display: none; }
.feedback.show { display: block; }
.feedback.ok { background: var(--ok-soft); color: var(--ok); }
.feedback.bad { background: var(--bad-soft); color: var(--bad); }
.feedback.info { background: var(--warn-soft); color: var(--warn); }
.feedback b { font-weight: 700; }

.hintbox { margin-top: 14px; display: grid; gap: 8px; }
.hint {
  background: var(--panel-2); border-left: 2px solid var(--accent);
  padding: 11px 16px; border-radius: 0 12px 12px 0; font-size: 14px; color: var(--ink-2);
}
.hint .n { font-size: 10px; letter-spacing: .16em; text-transform: uppercase; color: var(--ink-3); display: block; }

.solution { margin-top: 16px; display: none; }
.solution.show { display: block; }
.solution h3 { margin: 0 0 12px; }
.steps { display: grid; gap: 8px; counter-reset: step; }
.step {
  background: var(--panel-2); border: 1px solid var(--line-soft);
  border-radius: 12px; padding: 11px 16px;
  display: flex; gap: 14px; align-items: center; overflow-x: auto;
}
.step::before {
  counter-increment: step; content: counter(step);
  flex: 0 0 24px; height: 24px; border-radius: 999px;
  border: 1px solid color-mix(in srgb, var(--accent) 40%, transparent);
  background: var(--accent-soft); color: var(--accent);
  font-family: var(--serif); font-size: 12px; display: grid; place-items: center; font-weight: 700;
}
.final {
  margin-top: 14px; padding: 15px 18px; border-radius: 14px;
  background: var(--ok-soft); color: var(--ok); font-size: 19px; overflow-x: auto;
  display: flex; align-items: center; gap: 14px;
}
.final .lab { font-size: 10px; letter-spacing: .16em; text-transform: uppercase; opacity: .8; flex: 0 0 auto; }

/* ---------------------------------------------------------------- 통계 */
.grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 12px; }
.stat { background: var(--panel-2); border: 1px solid var(--line-soft); border-radius: 14px; padding: 16px 18px; }
.stat .v { font-family: var(--serif); font-size: 30px; font-weight: 700; font-variant-numeric: tabular-nums; letter-spacing: -.02em; line-height: 1.3; }
.stat .sub { font-size: 11.5px; color: var(--ink-3); }

.bar { height: 6px; border-radius: 999px; background: var(--line-soft); overflow: hidden; margin-top: 9px; }
.bar > i { display: block; height: 100%; background: var(--accent); border-radius: 999px; }

/* ---------------------------------------------------------------- 아카이브 */
.archive-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(96px, 1fr)); gap: 8px; }
.day {
  border: 1px solid var(--line); background: var(--panel); border-radius: 14px;
  padding: 11px 8px; text-align: center; font-size: 12px; color: var(--ink-2);
  box-shadow: var(--lift); transition: transform .15s, border-color .15s;
}
.day:hover { border-color: var(--accent); transform: translateY(-2px); }
.day .d { font-family: var(--serif); font-size: 17px; font-weight: 700; color: var(--ink); font-variant-numeric: tabular-nums; }
.day .m { font-size: 10px; letter-spacing: .1em; color: var(--ink-3); }
.day .marks { margin-top: 4px; letter-spacing: 1px; font-size: 11px; }
.day.today { border-color: var(--accent); box-shadow: var(--lift), 0 0 0 4px var(--accent-soft); }
.day.done .d { color: var(--ok); }

/* 관리자 키가 없으면 지난 날짜는 잠긴다 */
.day.locked { background: var(--panel-2); box-shadow: none; border-style: dashed; }
.day.locked .d, .day.locked .m { color: var(--ink-3); }
.day.locked .marks { color: var(--ink-3); opacity: .5; }
.day.locked:hover { border-color: var(--line); transform: none; }

.muted { color: var(--ink-3); font-size: 13px; }
.hidden { display: none !important; }

footer { text-align: center; color: var(--ink-3); font-size: 12px; letter-spacing: .08em; padding-top: 12px; }
footer b { font-family: var(--serif); }
/* 관리자 키는 평소에 눈에 띌 필요가 없어 맨 아래에 작게 둔다 */
footer .keylink {
  display: block; margin: 10px auto 0; padding: 4px 8px;
  font: inherit; font-size: 10.5px; letter-spacing: .06em;
  background: none; border: 0; cursor: pointer;
  color: var(--ink-3); opacity: .55;
  transition: opacity .15s, color .15s;
}
footer .keylink:hover, footer .keylink:focus-visible { opacity: 1; color: var(--accent); }

@media (max-width: 620px) {
  header.top { gap: 7px; }
  .brand { gap: 8px; }
  .brand .sym { width: 36px; height: 36px; flex-basis: 36px; font-size: 20px; }
  .brand h1 { font-size: 17px; }
  .pill { padding: 6px 11px; font-size: 11.5px; gap: 5px; }
  .icon-btn { width: 36px; height: 36px; }
  #hubView { min-height: min(60vh, 430px); }
  .hub { --hub-max: 336px; }
  .hub-core .word { font-size: clamp(24px, 8.5vw, 34px); }
  .hub-core .kicker { font-size: 13px; }
  .orb .ball { font-size: 20px; }
  .orb .lab { font-size: 10.5px; letter-spacing: .05em; }
  .problem { font-size: 25px; }
  .brand .tag { display: none; }
  .card { padding: 18px; }
}

/* ---------------------------------------------------------------- 연습장 */

/* 전체 화면을 덮는 필기판. 문제를 위에 띄워 두고 그 아래에 손으로 푼다. */
.pad {
  position: fixed; inset: 0; z-index: 60;
  display: flex; flex-direction: column;
  background: var(--bg);
  overscroll-behavior: contain;
}
body.pad-open { overflow: hidden; }

.pad-bar {
  display: flex; align-items: center; gap: 10px;
  padding: 10px 14px; border-bottom: 1px solid var(--line);
  background: var(--panel); backdrop-filter: blur(8px);
}
/* 문제는 한 줄로 눕혀 둔다 — 길면 가로로만 넘긴다 */
.pad-prob {
  min-width: 0; flex: 1 1 auto;
  overflow-x: auto; overflow-y: hidden;
  font-size: 19px; white-space: nowrap;
  scrollbar-width: thin;
}
.pad-prob .katex-display { margin: 0; }
.pad-prob .katex-display > .katex { text-align: left; }

.pad-tools {
  display: flex; align-items: center; flex-wrap: wrap; gap: 6px;
  padding: 8px 14px; border-bottom: 1px solid var(--line-soft);
  background: var(--panel-2);
}
.pad-tools .spacer { flex: 1 1 auto; }
.tool {
  font: inherit; font-size: 12px; font-weight: 500;
  padding: 7px 12px; border-radius: 999px;
  border: 1px solid var(--line); background: var(--panel);
  color: var(--ink-2); cursor: pointer;
  transition: border-color .15s, color .15s, background .15s;
}
.tool:hover { border-color: var(--accent); color: var(--ink); }
.tool.on { border-color: var(--accent); color: var(--accent); background: var(--accent-soft); }
.tool.pen-only.on { border-color: var(--ok); color: var(--ok); background: var(--ok-soft); }
.tool-sep { width: 1px; height: 20px; background: var(--line); margin: 0 2px; }

.swatches, .widths { display: flex; align-items: center; gap: 5px; }
.swatch {
  width: 24px; height: 24px; padding: 0; border-radius: 50%;
  border: 2px solid transparent; background: none; cursor: pointer;
  display: grid; place-items: center;
}
.swatch i { display: block; width: 15px; height: 15px; border-radius: 50%;
            box-shadow: inset 0 0 0 1px rgba(0, 0, 0, .18); }
.swatch.on { border-color: var(--accent); }

.wbtn {
  width: 26px; height: 26px; padding: 0; border-radius: 50%;
  border: 1px solid var(--line); background: var(--panel); cursor: pointer;
  display: grid; place-items: center;
}
.wbtn i { display: block; border-radius: 50%; background: var(--ink-2); }
.wbtn.on { border-color: var(--accent); background: var(--accent-soft); }
.wbtn.on i { background: var(--accent); }

/* 캔버스가 얹히는 모눈종이 */
.pad-sheet {
  position: relative; flex: 1 1 auto; min-height: 0;
  background-color: var(--panel-solid);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 28px 28px;
  background-position: center top;
}
/* touch-action 을 꺼야 펜이 스크롤로 먹히지 않는다.
   손가락 입력은 자바스크립트에서 걸러내므로 손바닥이 닿아도 선이 그어지지 않는다. */
#padCanvas { position: absolute; inset: 0; width: 100%; height: 100%;
             touch-action: none; cursor: crosshair; }

/* 화면 어디서든 쓰는 알림. 연습장(z-index 60) 위에 떠야 한다. */
.toast {
  position: fixed; z-index: 70;
  left: 50%; bottom: 26px; transform: translateX(-50%) translateY(8px);
  max-width: min(90%, 420px);
  padding: 10px 16px; border-radius: 999px;
  background: var(--panel); border: 1px solid var(--line); box-shadow: var(--lift);
  backdrop-filter: blur(8px);
  font-size: 12.5px; color: var(--ink-2); text-align: center;
  opacity: 0; pointer-events: none; transition: opacity .2s, transform .2s;
}
.toast.show { opacity: 1; transform: translateX(-50%) translateY(0); }

@media (max-width: 560px) {
  .pad-bar { padding: 8px 10px; }
  /* 좁은 화면에서는 수식에 자리를 다 내준다 */
  .pad-bar > .chip { display: none; }
  .pad-prob { font-size: 16px; }
  .pad-tools { padding: 7px 10px; gap: 5px; }
  .tool { padding: 6px 10px; font-size: 11.5px; }
}

@media (prefers-reduced-motion: reduce) {
  .orb .ball, .btn, .day, .icon-btn, .levels button, .palette button, .orb-back { transition: none; }
  .hub-ring, .orb .spin { transition: none; }
  .tool, .toast, footer .keylink { transition: none; }
}