:root {
  font-family: Inter, system-ui, sans-serif;
  font-optical-sizing: auto;
  font-synthesis: none;
  line-height: 1.5;
  color: #e7eaf0;
  background: #10131a;
  text-rendering: optimizeLegibility;
}

* {
  box-sizing: border-box;
}

body {
  min-width: 320px;
  margin: 0;
}

.workbench {
  width: min(100% - 32px, 960px);
  padding: 40px 0;
  margin: 0 auto;
}

.page-header {
  margin-bottom: 28px;
}

.page-header h1 {
  margin: 0 0 8px;
  font-size: clamp(2rem, 5vw, 3rem);
  letter-spacing: -0.04em;
}

.page-header p,
.hint,
.empty-state {
  color: #9ba5b5;
}

.panel {
  padding: 24px;
  margin-bottom: 20px;
  background: #191e28;
  border: 1px solid #303744;
  border-radius: 14px;
}

.panel h2 {
  margin-top: 0;
  font-size: 1.1rem;
}

label {
  display: block;
  margin-bottom: 10px;
  font-weight: 600;
}

textarea {
  display: block;
  width: 100%;
  padding: 14px;
  font: inherit;
  font-family: ui-monospace, monospace;
  color: inherit;
  resize: vertical;
  background: #10131a;
  border: 1px solid #414b5d;
  border-radius: 8px;
}

textarea:focus {
  outline: 2px solid #7c8cff;
  outline-offset: 2px;
}

.actions {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  margin-top: 14px;
}

button {
  padding: 11px 18px;
  font-weight: 700;
  color: #10131a;
  cursor: pointer;
  background: #9ba7ff;
  border: 0;
  border-radius: 8px;
}

button:hover {
  filter: brightness(1.08);
}

button.secondary {
  color: #e7eaf0;
  background: transparent;
  border: 1px solid #414b5d;
}

.expression {
  padding: 14px;
  margin: 0;
  font:
    1rem / 1.7 ui-monospace,
    monospace;
  color: #b9c5ff;
  overflow-wrap: anywhere;
  white-space: pre-wrap;
  background: #10131a;
  border-radius: 8px;
}

.error {
  color: #ff9292;
}

#history li {
  margin: 12px 0;
}

.step-rule {
  display: block;
  margin-bottom: 4px;
  font-weight: 700;
  color: #9ba7ff;
}

@media (max-width: 600px) {
  .workbench {
    padding-top: 24px;
  }

  .panel {
    padding: 16px;
  }
}

.tree {
  --tree-bg: #111620;
  --node-bg: #202838;
  --node-border: #3b475c;
  --operator-bg: #252d49;
  --operator-border: #8190ff;
  --operator-color: #c5ccff;
  --variable-bg: #18352f;
  --variable-border: #3a8f76;
  --variable-color: #9ce8cf;
  --connector: #536079;
  --tree-text: #e7eaf0;

  display: block;
  width: 100%;
  min-height: 160px;
  padding: 32px 24px;
  overflow: auto;
  scrollbar-color: #46516a transparent;
  scrollbar-width: thin;
  background: radial-gradient(circle, #303b50 1px, transparent 1.2px);
  background-color: var(--tree-bg);
  background-size: 22px 22px;
  border: 1px solid #2d3748;
  border-radius: 12px;
}

/* Root node and all nested branches */

.tree-branch {
  position: relative;
  display: flex;
  flex: 0 0 auto;
  flex-direction: column;
  align-items: center;
  width: max-content;
  min-width: 48px;
  padding: 0;
}

/* Node appearance */

.tree-node {
  position: relative;
  z-index: 1;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-width: 52px;
  min-height: 42px;
  padding: 9px 16px;

  font-family: "SFMono-Regular", Consolas, monospace;
  font-size: 14px;
  font-weight: 650;
  color: var(--tree-text);
  letter-spacing: 0.02em;
  white-space: nowrap;
  background: linear-gradient(145deg, #252e3e, var(--node-bg));

  border: 1px solid var(--node-border);
  border-radius: 10px;

  box-shadow:
    0 3px 8px rgb(0 0 0 / 18%),
    inset 0 1px rgb(255 255 255 / 4%);

  transition:
    border-color 160ms ease,
    background 160ms ease,
    transform 160ms ease,
    box-shadow 160ms ease;
}

/* Boolean operators */

.tree-node.operator {
  color: var(--operator-color);
  background: linear-gradient(145deg, #303b61, var(--operator-bg));
  border-color: var(--operator-border);
  box-shadow:
    0 3px 12px rgb(94 111 255 / 12%),
    inset 0 1px rgb(255 255 255 / 7%);
}

/* Variables and constants */

.tree-node:not(.operator) {
  color: var(--variable-color);
  background: linear-gradient(145deg, #20483e, var(--variable-bg));
  border-color: var(--variable-border);
}

/* Child node layout */

.tree-children {
  position: relative;
  display: flex;
  gap: 32px;
  align-items: flex-start;
  justify-content: center;
  padding-top: 34px;
}

/* Vertical connector from parent to child row */

.tree-branch > .tree-children::before {
  position: absolute;
  top: 0;
  left: 50%;
  height: 17px;
  content: "";
  border-left: 1.5px solid var(--connector);
  transform: translateX(-50%);
}

/* Vertical connector from the child row to each child */

.tree-children > .tree-branch::before {
  position: absolute;
  top: -17px;
  left: 50%;
  height: 17px;
  content: "";
  border-left: 1.5px solid var(--connector);
}

/* Horizontal bar joining sibling branches */

.tree-children:has(> .tree-branch:nth-child(2))::after {
  position: absolute;
  top: 16px;
  left: calc(50% - 1px);
  width: 0;
  height: 0;
  content: "";
}

/* Draw horizontal connectors between two or more children */

.tree-children:has(> .tree-branch:nth-child(2)) > .tree-branch:first-child::after,
.tree-children:has(> .tree-branch:nth-child(2)) > .tree-branch:last-child::after {
  position: absolute;
  top: -18px;
  height: 1.5px;
  content: "";
  background: var(--connector);
}

.tree-children:has(> .tree-branch:nth-child(2)) > .tree-branch:first-child::after {
  right: -16px;
  left: 50%;
}

.tree-children:has(> .tree-branch:nth-child(2)) > .tree-branch:last-child::after {
  right: 50%;
  left: -16px;
}

/* NOT is a unary operator, so don't draw a sibling bar */

.tree-children:not(:has(> .tree-branch:nth-child(2))) {
  gap: 0;
}

/* Hover feedback */

.tree-node:hover {
  border-color: #a5b0ff;
  box-shadow: 0 6px 16px rgb(0 0 0 / 22%);
  transform: translateY(-2px);
}

.tree-node.operator:hover {
  background: linear-gradient(145deg, #394773, #292f50);
}

/* Keyboard accessibility if nodes become interactive later */

.tree-node:focus-visible {
  outline: 2px solid #a5b0ff;
  outline-offset: 4px;
}

/* Small screens */

@media (max-width: 600px) {
  .tree {
    padding: 28px 18px;
  }

  .tree-children {
    gap: 22px;
    padding-top: 30px;
  }

  .tree-node {
    min-width: 44px;
    min-height: 38px;
    padding: 8px 12px;
    font-size: 13px;
  }
}

@media (prefers-reduced-motion: reduce) {
  .tree-node {
    transition: none;
  }
}

.structure-header {
  display: flex;
  gap: 16px;
  align-items: flex-start;
  justify-content: space-between;
  margin-bottom: 22px;
}

.structure-header h2 {
  margin-bottom: 6px;
}

.structure-header p {
  margin: 0;
}

.status-pill {
  flex-shrink: 0;
  padding: 5px 10px;
  font-size: 12px;
  font-weight: 700;
  color: #b9c5ff;
  background: #202838;
  border: 1px solid #3b475c;
  border-radius: 999px;
}

.expression-comparison {
  display: grid;
  /* grid-template-columns: minmax(0, 1fr) 42px minmax(0, 1fr); */
  grid-template-columns: minmax(0, 1fr);
  gap: 12px;
  align-items: stretch;
}

.expression-side {
  min-width: 0;
  overflow: hidden;
  background: #111620;
  border: 1px solid #303b50;
  border-radius: 12px;
}

.side-heading {
  display: flex;
  gap: 9px;
  align-items: center;
  padding: 14px 16px;
  background: #191e28;
  border-bottom: 1px solid #303b50;
}

.side-heading h3 {
  margin: 0;
  font-size: 13px;
  font-weight: 700;
}

.side-indicator {
  width: 8px;
  height: 8px;
  border-radius: 50%;
}

.start-indicator {
  background: #9ba7ff;
  box-shadow: 0 0 12px #7c8cff66;
}

.end-indicator {
  background: #5dd6a3;
  box-shadow: 0 0 12px #5dd6a366;
}

.comparison-divider {
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 24px;
  color: #8190ff;
  
  transform: rotate(90deg);
}

.animation-tree {
  display: flex;
  align-items: flex-start;
  justify-content: center;
  height: 100%;
  min-height: 220px;
  padding: 26px 18px;
  overflow: auto;
  background-color: #111620;
  background-image: radial-gradient(circle, #303b50 1px, transparent 1.2px);
  background-size: 20px 20px;
  border: 0;
  border-radius: 0;
}

/* Animate only the start side */

#start-tree .tree-branch {
  animation: tree-enter 350ms cubic-bezier(0.2, 0.8, 0.2, 1) both;
}

#start-tree .tree-node {
  transition:
    border-color 220ms ease,
    background 220ms ease,
    box-shadow 220ms ease,
    transform 220ms ease;
}

#start-tree .tree-node.is-changing {
  background: #394773;
  border-color: #a5b0ff;
  box-shadow:
    0 0 0 4px #8190ff22,
    0 0 22px #8190ff22;
  transform: scale(1.06);
}

#start-tree .tree-node.is-settled {
  border-color: #5dd6a3;
  box-shadow: 0 0 0 3px #5dd6a31a;
}

/* Keep the final tree visually stable */

#end-tree .tree-branch,
#end-tree .tree-node {
  transform: none !important;
  transition: none !important;
  animation: none !important;
}

#end-tree .tree-node.operator {
  color: #9ce8cf;
  background: linear-gradient(145deg, #20483e, #18352f);
  border-color: #4c9f80;
}

/* Playback controls */

.playback-panel {
  padding: 18px;
  margin-bottom: 16px;
  background: #141923;
  border: 1px solid #303744;
  border-radius: 12px;
}

.playback-rule {
  display: grid;
  gap: 6px;
  margin-bottom: 20px;
}

.playback-rule .hint {
  margin: 0;
  font-size: 10px;
  font-weight: 800;
  letter-spacing: 0.1em;
}

.playback-rule strong {
  font-size: 15px;
  color: #c5ccff;
}

.playback-rule p {
  margin: 0;
  font-size: 13px;
  color: #9ba5b5;
  overflow-wrap: anywhere;
}

.playback-progress {
  display: grid;
  gap: 9px;
  margin-bottom: 18px;
  font-size: 12px;
  color: #9ba5b5;
}

.progress-track {
  height: 5px;
  overflow: hidden;
  background: #303744;
  border-radius: 99px;
}

.progress-fill {
  width: 0;
  height: 100%;
  background: linear-gradient(90deg, #8190ff, #5dd6a3);
  border-radius: inherit;
  transition: width 250ms ease;
}

.playback-controls {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
}

.playback-controls button {
  min-height: 40px;
}

.playback-controls button:disabled {
  cursor: not-allowed;
  opacity: 0.35;
  filter: none;
}

#play-button {
  min-width: 100px;
}

.speed-control {
  display: flex;
  gap: 8px;
  align-items: center;
  margin-left: auto;
  font-size: 12px;
  color: #9ba5b5;
}

.speed-control select {
  max-width: 110px;
  padding: 8px;
  font: inherit;
  color: #e7eaf0;
  background: #10131a;
  border: 1px solid #414b5d;
  border-radius: 7px;
}

/* Tree entrance animation */

@keyframes tree-enter {
  from {
    opacity: 0;
    transform: translateY(8px) scale(0.98);
  }
  to {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
}

@media (max-width: 700px) {
  .expression-comparison {
    grid-template-columns: minmax(0, 1fr);
  }

  .comparison-divider {
    height: 28px;
    transform: rotate(90deg);
  }

  .animation-tree {
    min-height: 160px;
  }

  .speed-control {
    width: 100%;
    margin: 4px 0 0;
  }
}

@media (prefers-reduced-motion: reduce) {
  #start-tree .tree-branch,
  #start-tree .tree-node,
  .progress-fill {
    transition: none !important;
    animation: none !important;
  }
}