.problem-main {
  width: min(var(--max), calc(100% - var(--page-gutter)));
  margin: 0 auto;
  padding: 34px 0 70px;
}

.problem-hero {
  padding: 28px 0 22px;
}

.problem-back-btn {
  display: inline-flex;
  align-items: center;
  min-height: 34px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--card);
  color: var(--muted);
  padding: 0 12px;
  font-size: 0.78rem;
  font-weight: 850;
  text-decoration: none;
}

.problem-back-btn:hover {
  background: var(--surface-hover);
  color: var(--text);
}

.problem-title-row {
  margin-top: 12px;
}

.problem-title-row h1 {
  max-width: 820px;
  margin: 10px 0 12px;
  font-size: clamp(2rem, 4.6vw, 3.45rem);
  line-height: 1.08;
  letter-spacing: 0;
}

.practice-hub-title {
  font-size: clamp(1.7rem, 3.4vw, 2.35rem) !important;
}

.problem-hero p:not(.career-kicker) {
  max-width: 780px;
  color: var(--muted);
  line-height: 1.65;
  font-size: clamp(0.98rem, 1.7vw, 1.08rem);
}

.problem-meta {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 18px;
}

.problem-meta span {
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 7px 11px;
  color: var(--muted);
  font-size: 0.78rem;
  font-weight: 800;
}

.practice-filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  margin-top: 18px;
}

.practice-filter-bar button {
  min-height: 34px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--card);
  color: var(--muted);
  padding: 0 13px;
  font-size: 0.78rem;
  font-weight: 850;
}

.practice-filter-bar button.active,
.practice-filter-bar button:hover {
  border-color: rgba(46, 229, 139, 0.36);
  background: var(--surface-hover);
  color: var(--accent);
}

.timer-shell {
  position: relative;
  flex: 0 0 auto;
  margin-left: auto;
}

.timer-pill {
  min-height: 38px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--card);
  color: var(--text);
  padding: 0 14px;
  font-size: 0.82rem;
  font-weight: 900;
}

.timer-pill.active {
  border-color: rgba(46, 229, 139, 0.52);
  color: var(--accent);
}

.timer-menu {
  position: absolute;
  top: calc(100% + 8px);
  right: 0;
  width: 220px;
  border: 1px solid var(--border);
  border-radius: 14px;
  background: var(--card);
  box-shadow: var(--shadow);
  padding: 10px;
  display: none;
  z-index: 20;
}

.timer-menu.show {
  display: grid;
  gap: 8px;
}

.timer-presets {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
}

.timer-presets button,
.timer-actions button {
  border: 1px solid var(--border);
  border-radius: 10px;
  background: transparent;
  color: var(--text);
  min-height: 34px;
  font-size: 0.78rem;
  font-weight: 850;
}

.timer-presets button:hover,
.timer-actions button:hover {
  background: var(--surface-hover);
}

.timer-custom {
  display: grid;
  gap: 6px;
  color: var(--muted);
  font-size: 0.74rem;
  font-weight: 800;
}

.timer-custom input {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface-input);
  color: var(--text);
  padding: 8px 10px;
}

.timer-actions {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 8px;
}

.timer-status {
  margin: 0;
  color: var(--muted);
  font-size: 0.76rem;
  line-height: 1.35;
}

.problem-layout {
  display: grid;
  grid-template-columns: minmax(0, 1fr) 260px;
  gap: 18px;
  align-items: start;
}

.problem-layout.related-hidden {
  grid-template-columns: minmax(0, 1fr);
}

.problem-layout.related-hidden .problem-side {
  display: none;
}

.problem-panel,
.problem-side,
.practice-problem-card {
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--card);
}

.problem-panel {
  overflow: hidden;
}

.problem-panel-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 6px;
  padding: 10px;
  border-bottom: 1px solid var(--border);
}

.problem-tabs {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}

.problem-tabs button {
  min-height: 34px;
  border: 1px solid transparent;
  border-radius: 999px;
  background: transparent;
  color: var(--muted);
  padding: 0 12px;
  font-size: 0.8rem;
  font-weight: 850;
}

.problem-tabs button.active,
.problem-tabs button:hover {
  border-color: rgba(46, 229, 139, 0.28);
  background: var(--surface-hover);
  color: var(--text);
}

.problem-tab-panel {
  display: none;
  padding: 22px;
}

.problem-tab-panel.active {
  display: block;
}

.problem-tab-panel h2,
.problem-tab-panel h3 {
  margin: 0 0 12px;
  letter-spacing: 0;
}

.problem-tab-panel h2 {
  font-size: 1.18rem;
}

.problem-tab-panel h3 {
  font-size: 0.98rem;
  margin-top: 18px;
}

.problem-tab-panel p,
.problem-tab-panel li {
  color: var(--muted);
  line-height: 1.65;
}

.problem-tab-panel ul,
.problem-tab-panel ol {
  padding-left: 20px;
}

.problem-code-block {
  position: relative;
  margin: 14px 0;
}

.problem-code-block pre {
  margin: 0;
  max-width: 100%;
  overflow: auto;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface-input);
  padding: 16px;
  color: var(--text);
  font-size: 0.82rem;
  line-height: 1.55;
}

.practice-warning {
  border: 1px solid rgba(248, 201, 107, 0.34);
  border-radius: 10px;
  background: rgba(248, 201, 107, 0.08);
  color: var(--warn) !important;
  padding: 10px 12px;
  font-weight: 850;
}

.practice-code-editor {
  width: 100%;
  min-height: 360px;
  resize: vertical;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface-input);
  color: var(--text);
  padding: 16px;
  font-family: Consolas, "SFMono-Regular", "Liberation Mono", monospace;
  font-size: 0.86rem;
  line-height: 1.55;
}

.practice-run-actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 12px;
}

.practice-run-actions .primary-btn,
.practice-run-actions .outline-btn {
  min-height: 40px;
  padding: 0 16px;
  font-size: 0.84rem;
}

.practice-run-output {
  display: grid;
  gap: 8px;
  margin-top: 14px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface-input);
  padding: 14px;
}

.practice-run-output.pass {
  border-color: rgba(46, 229, 139, 0.42);
}

.practice-run-output.fail {
  border-color: rgba(255, 107, 107, 0.42);
}

.practice-run-output strong {
  color: var(--text);
}

.practice-run-output span,
.practice-run-output li {
  color: var(--muted);
  line-height: 1.5;
  font-size: 0.84rem;
}

.practice-run-output ul {
  margin: 0;
  padding-left: 18px;
}

.copy-code-btn {
  position: absolute;
  top: 8px;
  right: 8px;
  border: 1px solid var(--border);
  border-radius: 999px;
  background: var(--card);
  color: var(--text);
  padding: 6px 10px;
  font-size: 0.72rem;
  font-weight: 850;
}

.problem-side {
  padding: 16px;
}

.problem-side strong {
  display: block;
  margin-bottom: 12px;
}

.problem-side a {
  display: block;
  border-top: 1px solid var(--border);
  padding: 11px 0;
  color: var(--muted);
  text-decoration: none;
  font-size: 0.84rem;
  font-weight: 780;
}

.problem-side a:hover {
  color: var(--accent);
}

.practice-problem-card {
  display: grid;
  grid-template-columns: 52px minmax(0, 1fr) auto;
  gap: 14px;
  align-items: center;
  min-height: 76px;
  padding: 14px;
  color: var(--text);
  text-decoration: none;
}

.practice-problem-card:hover {
  border-color: rgba(46, 229, 139, 0.36);
  background: var(--surface-hover);
}

.practice-problem-card.is-filtered-out {
  display: none;
}

.practice-problem-card[hidden] {
  display: none;
}

.practice-problem-card + .practice-problem-card {
  margin-top: 10px;
}

.practice-problem-card .prep-code {
  width: 42px;
}

.practice-problem-card strong {
  display: block;
  margin-bottom: 4px;
  font-size: 0.96rem;
}

.practice-problem-card span:not(.prep-code) {
  color: var(--muted);
  font-size: 0.84rem;
  line-height: 1.4;
}

.practice-problem-card small {
  color: var(--accent);
  font-size: 0.78rem;
  font-weight: 900;
}

@media (max-width: 860px) {
  .problem-layout {
    grid-template-columns: 1fr;
  }

  .problem-title-row {
    display: block;
  }

  .timer-shell {
    width: fit-content;
    margin-left: 0;
  }

  .timer-menu {
    left: 0;
    right: auto;
  }
}

@media (max-width: 640px) {
  .problem-main {
    width: min(var(--max), calc(100% - 44px));
    padding-top: 24px;
  }

  .problem-title-row h1 {
    font-size: clamp(1.52rem, 8vw, 1.9rem);
  }

  .practice-problem-card {
    grid-template-columns: 44px minmax(0, 1fr);
  }

  .practice-problem-card small {
    grid-column: 1 / -1;
  }

  .problem-tab-panel {
    padding: 16px;
  }
}

/* ============================================================
   Practice Waveform Simulation & Oscilloscope Viewer
   ============================================================ */

.practice-waveform-card {
  margin-top: 18px;
  border: 1px solid rgba(46, 229, 139, 0.28);
  border-radius: 12px;
  background: radial-gradient(circle at top left, #101a20, #090e13);
  padding: 18px;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.45);
}

.practice-waveform-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 10px;
  margin-bottom: 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid rgba(255, 255, 255, 0.08);
}

.practice-waveform-title {
  display: flex;
  align-items: center;
  gap: 8px;
}

.waveform-dot {
  width: 8px;
  height: 8px;
  border-radius: 50%;
  background: #2ee58b;
  box-shadow: 0 0 10px #2ee58b;
  display: inline-block;
  animation: pulse-dot 2s infinite ease-in-out;
}

@keyframes pulse-dot {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.4; transform: scale(0.85); }
}

.practice-waveform-title strong {
  color: #f1f7f4;
  font-size: 0.94rem;
  letter-spacing: 0.2px;
}

.waveform-meta {
  color: #8da499;
  font-size: 0.78rem;
  font-weight: 700;
}

.practice-waveform-scroll {
  overflow-x: auto;
  padding: 8px 4px 12px;
  scrollbar-width: thin;
  scrollbar-color: rgba(46, 229, 139, 0.3) rgba(0, 0, 0, 0.2);
}

.practice-waveform-scroll::-webkit-scrollbar {
  height: 6px;
}

.practice-waveform-scroll::-webkit-scrollbar-thumb {
  background: rgba(46, 229, 139, 0.3);
  border-radius: 999px;
}

.waveform-svg {
  display: block;
  min-width: 600px;
  font-family: Consolas, "SFMono-Regular", "Liberation Mono", monospace;
}

.practice-code-editor {
  tab-size: 2;
  -moz-tab-size: 2;
  font-family: Consolas, "SFMono-Regular", "Liberation Mono", Menlo, Courier, monospace !important;
  font-size: 0.88rem !important;
  line-height: 1.6 !important;
  background: #090e13 !important;
  color: #e2ede8 !important;
  border: 1px solid var(--border) !important;
  transition: border-color 0.15s ease, box-shadow 0.15s ease;
}

.practice-code-editor:focus {
  border-color: #2ee58b !important;
  box-shadow: 0 0 0 2px rgba(46, 229, 139, 0.18) !important;
  outline: none;
}