/* setting accents */

/* color accent trial */
:root {
  --accent: #8b5cf6;
  --accent-hover: #7c3aed;
  --accent-soft: rgba(139, 92, 246, 0.08);
  --accent-soft-strong: rgba(139, 92, 246, 0.16);
  --accent-text: #bfa9ff;
  --border-accent: rgba(139, 92, 246, 0.55);

  --bg-page: #1e1e1e;
  --bg-header: #252525;
  --bg-panel: #2a2a2a;
  --bg-panel-alt: #252525;
  --bg-input: #1e1e1e;
  --bg-code: #313131;
  --bg-button: #333333;
  --bg-button-hover: #444444;
  --bg-selected: #3a3a3a;
  --bg-disabled: #242424;
  --bg-button-alt: #303030;

  --icon-hover: #c4b5f8;

  --focus-border: #4fa3ff;
  --focus-ring: rgba(79, 163, 255, 0.25);

  --border-soft: #3a3a3a;
  --border-medium: #444444;
  --border-strong: #555555;
  --border-polymer: #666666;
  --border-monomer: #777777;

  --text-main: #e0e0e0;
  --text-heading: #dddddd;
  --text-muted: #bdbdbd;
  --text-subtle: #a0a0a0;
  --text-disabled: #777777;
  --text-inverse: #ffffff;

  --error-text: #e6b86c;
  --success-bg: #2f3a2f;
  --success-text: #b7e0b7;
  --danger-bg: #3a2a2a;
  --danger-text: #e07a7a;

  --shadow-panel: 0 2px 8px rgba(0,0,0,0.35);
  --shadow-panel-hover: 0 4px 14px rgba(0,0,0,0.45);
  --shadow-inset: inset 0 1px 0 rgba(255,255,255,0.03);
  --shadow-inset-hover: inset 0 1px 0 rgba(255,255,255,0.04);

  --scroll-thumb: #555555;
  --scroll-thumb-hover: #777777;
  --scroll-track: #252525;
}

body.theme-light {
  --accent: #4f3fb8;
  --accent-hover: #3f319a;
  --accent-soft: #e6e0ff;
  --accent-soft-strong: #d4c9ff;
  --accent-text: #31226f;
  --border-accent: #6d5bd6;

  --bg-page: #f4f4f5;
  --bg-header: #ffffff;
  --bg-panel: #ffffff;
  --bg-panel-alt: #f8f8fa;
  --bg-input: #ffffff;
  --bg-code: #f7f7f9;
  --bg-button: #f4f4f5;
  --bg-button-hover: #e9e9ec;
  --bg-selected: #ececf0;
  --bg-disabled: #ececf0;
  --bg-button-alt: #f1f1f3;

  --icon-hover: #5a48c8;

  --focus-border: #2563eb;
  --focus-ring: rgba(37, 99, 235, 0.18);

  --border-soft: #d6d6dc;
  --border-medium: #c4c4cc;
  --border-strong: #a8a8b3;
  --border-polymer: #9a9aa6;
  --border-monomer: #8a8a96;

  --text-main: #242428;
  --text-heading: #18181b;
  --text-muted: #4b4b55;
  --text-subtle: #686874;
  --text-disabled: #9a9aa3;
  --text-inverse: #111111;

  --error-text: #9a5b00;
  --success-bg: #e8f5e8;
  --success-text: #226622;
  --danger-bg: #f8e7e7;
  --danger-text: #a33a3a;

  --shadow-panel: 0 2px 8px rgba(0,0,0,0.08);
  --shadow-panel-hover: 0 4px 14px rgba(0,0,0,0.12);
  --shadow-inset: inset 0 1px 0 rgba(255,255,255,0.65);
  --shadow-inset-hover: inset 0 1px 0 rgba(255,255,255,0.8);

  --scroll-thumb: #b8b8c2;
  --scroll-thumb-hover: #9999a6;
  --scroll-track: #f1f1f3;
}


html, body {
  height: 100%;
}

body {
  margin: 0;
  font-family: system-ui, sans-serif;
  background: var(--bg-page);
  color: var(--text-main);
  padding-bottom: 0;
  overflow: hidden;

  display: flex;
  flex-direction: column;
}

header {
  position: relative;
  background: var(--bg-header);
  color: var(--text-inverse);
  padding: 1.5rem 2rem;
  border-bottom: 1px solid var(--border-soft);
  text-align: center; /* center the text */
}

header h1 {
  margin: 0;
  font-size: 2.35rem;  /* bigger */
  font-weight: 700;   /* slightly bold but not heavy */
  letter-spacing: 0.4px; /* subtle polish */
  color: var(--text-heading);
}

header h1::after {
  content: "";
  display: block;

  width: 72px;
  height: 3px;

  margin: 0.35rem auto 0;

  border-radius: 999px;
  background: var(--accent);
  opacity: 0.85;
}

.guide-link,
.about-link,
.theme-toggle-btn {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);

  width: 40px;
  height: 40px;
  padding: 0;

  display: inline-flex;
  align-items: center;
  justify-content: center;

  color: var(--text-muted);
  background: transparent;

  border: none;
  border-radius: 0;

  opacity: 0.85;
  text-decoration: none;
}

.about-link {
  right: 6.25rem;
}

.guide-link {
  right: 3.5rem;
}

.theme-toggle-btn {
  right: 0.75rem;
}

.guide-link:hover,
.about-link:hover,
.theme-toggle-btn:hover,
.theme-toggle-btn:hover:not(:disabled) {
  background: transparent;
  opacity: 1;
  color: var(--icon-hover);
}

.guide-link:hover svg,
.about-link:hover svg,
.theme-toggle-btn:hover svg,
.guide-link:hover svg path,
.about-link:hover svg path,
.theme-toggle-btn:hover svg path {
  stroke: var(--icon-hover);
}

.guide-link svg,
#home-link svg,
.theme-toggle-btn svg {
  width: 26px;
  height: 26px;
  pointer-events: none;
}

#about-link svg {
  width: 28px;
  height: 28px;
  pointer-events: none;
}

.page-layout {
  display: grid;
  grid-template-columns: 2fr 1fr;
  gap: 1rem;
  padding: 1rem;
  align-items: stretch;
  flex: 1;
  min-height: 0;
  overflow: hidden;
}
@media (max-width: 900px) {
  .page-layout {
    grid-template-columns: 1fr;
  }
}

.input-panel{
  position: relative;
}

.input-panel,
.display-panel {
  min-height: 0;
  overflow: auto;
}

.input-panel,
.display-panel,
.control-panel {
  background: var(--bg-panel);
  border-radius: 8px;
  padding: 1rem;
  border: 1px solid var(--border-soft);
}

.collapse-input-btn {
  position: absolute;
  top: 0.55rem;
  right: 0.55rem;
  width: 32px;
  height: 32px;
  padding: 0;
  z-index: 5;
}

.page-layout.input-collapsed {
  grid-template-columns: 35px 1fr;
}

.page-layout.input-collapsed .input-panel > :not(#collapse-input-btn) {
  display: none;
}

.page-layout.input-collapsed .input-panel {
  padding: 0;
  border: none;
  background: transparent;
  overflow: visible;
}

.page-layout.input-collapsed #collapse-input-btn {
  position: absolute;
  left: 0.75rem;
  top: 0.75rem;
}

.input-block {
  margin-bottom: 1.5rem;
}

h2 {
  margin-top: 0;
  color: var(--text-heading);
}


.input-panel.has-collapse-btn > .example-selection {
  margin-top: 1.75rem;
}

.example-selection {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;

  margin-bottom: 0.85rem;
  margin-top: 0;
  padding: 0.75rem;

  background: var(--bg-panel-alt);
  border: 1px solid var(--border-soft);
  border-radius: 8px;
}

.example-selection label {
  font-size: 0.8rem;
  color: var(--text-subtle);
}

.example-selection select {
  width: 100%;
  max-width: 220px;

  padding: 0.45rem 0.6rem;

  background: var(--bg-input);
  color: var(--text-main);

  border: 1px solid var(--border-medium);
  border-radius: 6px;

  font-size: 0.9rem;
}

.example-selection select:disabled {
  opacity: 0.55;
  cursor: not-allowed;
}

.example-code {
  background: var(--bg-code);   /* lighter than panel (var(--bg-panel)) */
  color: var(--text-main);
  padding: 0.75rem;
  border-radius: 6px;
  font-family: monospace;
  font-size: 0.9rem;
  border: 1px solid var(--border-medium);
  box-shadow: var(--shadow-panel);
}

.example-wrapper {
  position: relative;
}

.fill-btn {
  position: absolute;
  top: 6px;
  right: 6px;
  font-size: 0.75rem;
  padding: 4px 8px;
  border: none;
  border-radius: 4px;
  background: var(--border-medium);
  color: var(--text-main);
  cursor: pointer;
}

.fill-btn:hover {
  background: var(--bg-button-hover);
}

.code-label {
  display: block;
  font-size: 0.75rem;
  color: var(--text-subtle);
  margin-bottom: 0.25rem;
}

textarea {
  width: 100%;
  min-height: 140px;
  font-family: monospace;
  font-size: 1rem;
  box-sizing: border-box;
  border: 1px solid var(--border-medium);
  border-radius: 6px;
  padding: 0.5rem;
  background: var(--bg-input);
  color: var(--text-main);

  resize: vertical;   /* nice UX */
}

.saved-config-row {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin: 0.5rem 0 0.75rem;
}

.saved-config-row label {
  color: var(--text-subtle);
  font-size: 0.85rem;
}

.saved-config-group {
  margin-left: auto;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}

#saved-config-select {
  min-width: 140px;
}

.error-inline {
  color: var(--error-text);
  font-size: 0.85rem;
  margin-bottom: 0.5rem;
}

textarea:disabled,
input:disabled,
select:disabled {
  background-color: var(--bg-disabled);
  opacity: 0.7;
  cursor: not-allowed;
}

textarea:focus,
select:focus,
input:focus {
  outline: none;
  border-color: var(--border-accent);
  box-shadow: 0 0 0 2px var(--accent-soft);
}

#w-input {
  width: 60px;         /* small by default */
  transition: width 0.2s ease;
}

#k-input {
  width: 60px;
}

.approach-block {
  display: flex;
  align-items: center;
  gap: 1rem;           /* more space between dropdown and input */
}

select,
input {
  padding: 0.4rem;
  font-size: 1rem;
  border: 1px solid var(--border-medium);
  border-radius: 5px;
  background: var(--bg-input);
  color: var(--text-main);
}

.control-panel {
  display: flex;
  flex-direction: row;
  gap: 0.75rem;
  flex-wrap: wrap;
  padding: 0.75rem 1rem;
  justify-content: center;
  align-items: center;

  margin: 0 1rem 1rem;
  padding: 0.5rem 0.75rem;

  background: var(--bg-header);
  border-radius: 8px;
  border: 1px solid var(--border-soft);
  min-height: 100px;

  box-sizing: border-box;
  flex-shrink: 0;
}

#start-controls,
#running-controls,
#paused-controls,
.persistent-controls {
  display: flex;
  gap: 0.75rem;
  align-items: center;
}

.persistent-controls {
  padding-left: 0.75rem;
  border-left: 1px solid var(--border-soft);
}

button {
  padding: 0.6rem;
  font-size: 1rem;
  border-radius: 6px;
  border: 1px solid var(--border-medium);
  background: var(--bg-button);
  color: var(--text-main);
  cursor: pointer;
  transition: background 0.2s ease;
}

button:hover:not(:disabled) {
  background: var(--bg-button-hover);
}

button:disabled {
  background: var(--bg-panel);
  color: var(--text-disabled);
  border-color: var(--bg-button);
  cursor: not-allowed;
}

/* #save-system-btn {
  background: var(--bg-selected);
  border-color: #666666;
  font-weight: 500;
}

#save-system-btn:hover:not(:disabled) {
  background: #4a4a4a
} */

.display-panel {
  display: flex;
  flex-direction: column;
}
/* configuration rendering */

.history-nav-btn {
  position: absolute;
  top: 50%;
  transform: translateY(-50%);

  width: 34px;
  height: 48px;

  display: flex;
  align-items: center;
  justify-content: center;

  padding: 0;

  border-radius: 8px;

  opacity: 0.55;
  z-index: 2;
}

.history-nav-btn:hover:not(:disabled) {
  opacity: 1;
}

.history-nav-btn:disabled {
  opacity: 0.2;
  cursor: not-allowed;
}

.history-nav-prev {
  left: 0.5rem;
}

.history-nav-next {
  right: 0.5rem;
}

.close-selected-config-btn {
  opacity: 0.65;
}

.close-selected-config-btn:hover {
  opacity: 1;
}

#configuration-output {
  flex: 1;
  min-height: 0;

  display: flex;
  flex-direction: column;

  background: var(--bg-panel-alt);
  border: 1px solid var(--border-soft);
  border-radius: 6px;
  padding: 1rem;
  color: var(--text-main);
  /* white-space: pre-wrap; */
  overflow-y: auto;
  overflow-x: hidden;          /* scroll if needed */
}

.configuration-view {
  flex: 1;
  min-width: 0;

  display: flex;
  flex-direction: column;

  gap: 0.75rem;

  border: 1px solid var(--border-soft);
  border-radius: 6px;
  padding: 0.75rem;
  background: var(--bg-panel-alt);

  box-shadow: 
    var(--shadow-panel),
    var(--shadow-inset);
  
  transition:
    border-color 0.2s ease,
    box-shadow 0.2s ease;
}

.configuration-view:hover {
  border-color: var(--border-medium);

  box-shadow:
    var(--shadow-panel-hover),
    var(--shadow-inset-hover);
}

#selected-config-view {
  position: relative;
}

#configuration-render-row {
  display: flex;
  gap: 1rem;
  align-items: stretch;
  flex: 0 0 auto;
}

#selected-render-area,
#configuration-render-area {
  display: flex;
  flex-direction: column;
  gap: 1rem;

  flex: 1;
  min-height: 0;
  max-height: min(40vh, 520px);
  overflow: auto;
}

.collapse-render-btn {
  align-self: flex-end;
  margin-bottom: 0.25rem;

  border-radius: 8px;
  background: var(--bg-button-alt);
  color: var(--text-muted);
  border: 1px solid var(--border-medium);
}

.collapse-render-btn:hover {
  background: var(--bg-selected);
  color: var(--text-inverse);
}

.collapse-render-btn svg {
  transition: transform 0.15s ease;
}

.configuration-view.render-collapsed .collapse-render-btn svg {
  transform: rotate(180deg);
}

.configuration-view.render-collapsed #configuration-render-area,
.configuration-view.render-collapsed #selected-render-area,
.configuration-view.render-collapsed .export-config-svg-btn {
  display: none;
}

#config-tabs-panel {
  flex: 0 0 auto;
}

.config-tabs {
  display: flex;
  gap: 0.35rem;

  margin-top: 0.75rem;
  margin-bottom: 0.5rem;
}

.config-tab {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;

  padding: 0.35rem 0.75rem;

  font-size: 0.9rem;
  font-weight: 500;

  border-radius: 6px 6px 0 0;

  background: var(--bg-panel);
  border: 1px solid var(--border-soft);

  color: var(--text-muted);

  min-height: unset;
}

.config-tabs:has(.config-tab:not(.hidden):only-child) {
  justify-content: flex-start;
}

.config-tabs .config-tab:only-child {
  min-width: 180px;
}

.config-tab:hover {
  background: var(--bg-button-hover);
}

.config-tab.active {
  background: var(--bg-selected);
  color: var(--text-heading);
  border-color: var(--border-medium);
}

.export-config-svg-btn {
  display: block;
  margin-left: auto;
  margin-top: 0.75rem;

  width: 36px;
  height: 32px;
  padding: 0;

  border: 1px solid var(--border-strong);
  border-radius: 8px;

  background: var(--bg-button-alt);
  color: var(--text-main);

  font-size: 0.85rem;
  cursor: pointer;
  opacity: 0.9;
}

.export-config-svg-btn:hover {
  background: var(--bg-selected);
  opacity: 1;
}

.export-config-svg-btn:active {
  transform: translateY(1px);
}

.config-label-row {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 0.75rem;
}

#selected-config-label-input,
#current-config-label-input {
  flex: 1;
  min-width: 0;
}

.icon-btn {
  width: 32px;
  height: 32px;
  padding: 0;

  display: flex;
  align-items: center;
  justify-content: center;

  font-size: 0.85rem;
  line-height: 1;
}

.icon-btn {
  opacity: 0.8;
}

.label-error {
  color: var(--error-text);
  font-size: 0.8rem;
  font-family: system-ui, sans-serif;
  margin-left: 0.35rem;
  white-space: nowrap;
}

.label-save-btn,
.label-cancel-btn {
  font-weight: 600;
}

.label-save-btn:hover {
  background: var(--success-bg);
  color: var(--success-text);
}

#next-btn:disabled{
  opacity: 0.45;
  cursor: not-allowed;
}

.saved-config-delete-btn {
  width: 24px;
  height: 24px;
  padding: 0;
  border: none;
  background: transparent;
  color: var(--text-subtle);
  opacity: 0.65;
}

.saved-config-delete-btn svg {
  width: 14px;
  height: 14px;
}

.saved-config-delete-btn:hover {
  background: var(--danger-bg);
  color: var(--danger-text);
  opacity: 1;
}

.icon-btn svg,
#close-history-tab-btn svg,
#close-saved-tab-btn svg,
#close-selected-config-btn svg,
.collapse-input-btn svg,
.collapse-render-btn svg {
  width: 14px;
  height: 14px;
  pointer-events: none;
}

.icon-btn:hover {
  opacity: 1;
}

#close-history-tab-btn,
#close-saved-tab-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;

  width: 24px;
  height: 24px;
  opacity: 0.65;
}

#close-history-tab-btn:hover,
#close-saved-tab-btn:hover {
  opacity: 1;
}

.hidden {
  display: none !important;
}

.config-canvas {
  display: flex;
  justify-content: center;
  align-items: flex-start;
  min-height: unset;
}

.configuration {
  border: 2px dashed var(--border-strong);
  border-radius: 10px;
  padding: 16px;

  display: flex;
  flex-direction: column;
  gap: 12px;

  min-width: 300px;
  max-width: 800px;
}

.polymer {
  border: 1.5px dashed var(--border-polymer);
  padding: 10px;
  margin: 0;
  border-radius: 8px;

  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  max-width: 320px;
  justify-content: center;
  align-items: center;
}

.monomer {
  border: 1px solid var(--border-monomer);
  padding: 6px 10px;
  border-radius: 6px;

  background: var(--bg-panel);
  color: var(--text-main);

  font-family: monospace;
  cursor: default;
}

.monomer:hover {
  background: var(--bg-selected);
}

.energy-display {
  margin-top: 1rem;
  text-align: center;
  color: var(--text-muted);
  font-family: monospace;
  font-size: 0.95rem;
}

#history-config-panel,
#saved-config-panel,
#next-config-panel {
  margin-top: 1rem;
  border-top: 1px solid var(--border-soft);
  padding-top: 0.75rem;
}

#history-config-list,
#saved-config-list,
#next-config-list {
  max-height: clamp(160px, 28vh, 260px);
  overflow-y: auto;

  border: 1px solid var(--border-soft);
  border-radius: 6px;
  background: var(--bg-input);
  padding: 0.5rem;

  font-family: monospace;
  font-size: 0.9rem;
}

.history-config-item,
.saved-config-item,
.next-config-item {
  padding: 0.5rem;
  border-radius: 5px;
  border: 1px solid transparent;
  cursor: pointer;

  display: flex;
  justify-content: space-between;
  gap: 1rem;
  align-items: center;

  white-space: pre-wrap;
  line-height: 1.35;
}

.history-config-body,
.next-config-body,
.saved-config-body {
  flex: 1;
}

.history-config-label,
.next-config-label,
.saved-config-label {
  font-size: 0.8rem;
  color: var(--text-heading);
  font-weight: 600;
  margin-bottom: 0.25rem;
}

.history-config-item.selected .history-config-label,
.saved-config-item.selected .saved-config-label,
.next-config-item.selected .next-config-label {
  color: var(--accent-text);
}

.history-config-text,
.next-config-text,
.saved-config-text {
  white-space: pre-wrap;
}

.guided-config-radio {
  appearance: none;

  width: 14px;
  height: 14px;

  margin: 0 0 0.6rem 0;
  align-self: center;

  border: 1.5px solid var(--border-strong);
  border-radius: 50%;

  background-color: var(--bg-panel-alt);

  cursor: pointer;
  flex-shrink: 0;
}

.guided-config-radio:checked {
  border-color: var(--text-muted);
  background:
    radial-gradient(circle, var(--text-muted) 0 40%, transparent 45%);
}

.guided-config-radio:hover {
  border-color: var(--border-monomer);
}

.guided-config-radio:focus-visible {
  outline: 2px solid var(--focus-ring);
  outline-offset: 2px;
}


.history-config-meta,
.saved-config-meta,
.next-config-meta {
  display: flex;
  flex-direction: column;
  align-items: flex-end;
  gap: 0.15rem;

  font-size: 0.8rem;
  color: var(--text-muted);
  font-family: monospace;
  white-space: nowrap;
}

.history-config-energy,
.saved-config-energy,
.next-config-count,
.next-config-probability,
.next-config-energy,
.next-config-w {
  opacity: 0.9;
}

.history-config-item:hover,
.saved-config-item:hover,
.next-config-item:hover {
  background: var(--bg-button);
}

.history-config-item.selected,
.saved-config-item.selected,
.next-config-item.selected {
  background: var(--accent-soft);
  border-color: var(--border-accent);
}

.next-config-divider-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;

  margin: 0.75rem 0;
}

.next-config-divider-row::before,
.next-config-divider-row::after {
  content: "";
  flex: 1;
  height: 1px;
  background: var(--border-soft);
}

.next-config-divider-btn {
  padding: 0.25rem 0.6rem;

  font-size: 0.8rem;
  font-family: monospace;

  color: var(--text-muted);
  background: var(--bg-panel-alt);

  border: 1px solid var(--border-soft);
  border-radius: 999px;

  white-space: nowrap;
}

.next-config-divider-btn:hover {
  background: var(--bg-button-hover);
}

.next-config-divider-label {
  padding: 0.25rem 0.6rem;

  font-size: 0.8rem;
  font-family: monospace;

  color: var(--text-muted);
  background: var(--bg-panel-alt);

  border: 1px solid var(--border-soft);
  border-radius: 999px;

  white-space: nowrap;
}

.control-panel button {
  position: relative;
}

.control-panel button::after {
  content: "";
  position: absolute;

  left: 12%;
  right: 12%;
  bottom: 4px;

  height: 2px;
  border-radius: 999px;

  background: var(--accent);

  transform: scaleX(0);
  transform-origin: center;
  transition: transform 0.18s ease;
}

.control-panel button:hover:not(:disabled)::after,
.control-panel button:focus-visible:not(:disabled)::after {
  transform: scaleX(1);
}

/* scroll bars prettier */
.about-page,
#configuration-render-area,
#selected-render-area,
#configuration-output,
.input-panel,
.display-panel,
#next-config-list,
#saved-config-list,
#history-config-list {
  scrollbar-width: thin;                 /* Firefox */
  scrollbar-color: var(--scroll-thumb) var(--scroll-track);         /* thumb track */
}

.about-page::-webkit-scrollbar,
#configuration-render-area::-webkit-scrollbar,
#selected-render-area::-webkit-scrollbar,
#configuration-output::-webkit-scrollbar,
.input-panel::-webkit-scrollbar,
.display-panel::-webkit-scrollbar,
#next-config-list::-webkit-scrollbar,
#saved-config-list::-webkit-scrollbar,
#history-config-list::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

.about-page::-webkit-scrollbar-track,
#configuration-render-area::-webkit-scrollbar-track,
#selected-render-area::-webkit-scrollbar-track,
#configuration-output::-webkit-scrollbar-track,
.input-panel::-webkit-scrollbar-track,
.display-panel::-webkit-scrollbar-track,
#next-config-list::-webkit-scrollbar-track,
#saved-config-list::-webkit-scrollbar-track,
#history-config-list::-webkit-scrollbar-track {
  background: var(--scroll-track);
}

.about-page::-webkit-scrollbar-thumb,
#configuration-render-area::-webkit-scrollbar-thumb,
#selected-render-area::-webkit-scrollbar-thumb,
#configuration-output::-webkit-scrollbar-thumb,
.input-panel::-webkit-scrollbar-thumb,
.display-panel::-webkit-scrollbar-thumb,
#next-config-list::-webkit-scrollbar-thumb,
#saved-config-list::-webkit-scrollbar-thumb,
#history-config-list::-webkit-scrollbar-thumb {
  background: var(--scroll-thumb);
  border-radius: 999px;
  border: 2px solid var(--scroll-track);
}

.about-page::-webkit-scrollbar-thumb:hover,
#configuration-render-area::-webkit-scrollbar-thumb:hover,
#selected-render-area::-webkit-scrollbar-thumb:hover,
#configuration-output::-webkit-scrollbar-thumb:hover,
.input-panel::-webkit-scrollbar-thumb:hover,
.display-panel::-webkit-scrollbar-thumb:hover,
#next-config-list::-webkit-scrollbar-thumb:hover,
#saved-config-list::-webkit-scrollbar-thumb:hover,
#history-config-list::-webkit-scrollbar-thumb:hover {
  background: var(--scroll-thumb-hover);
}

/* about page css */
.about-page {
  flex: 1;
  padding: 2rem;
  overflow: auto;
}

.about-card {
  max-width: 1000px;
  margin: 0 auto;

  background: var(--bg-panel);
  border: 1px solid var(--border-soft);
  border-radius: 10px;

  padding: 2rem;
  box-shadow: var(--shadow-panel);
}

.about-card h2 {
  margin-top: 1.75rem;
  padding-top: 1.25rem;
  border-top: 1px solid var(--border-soft);
  color: var(--text-heading);
}

.about-card h2:first-of-type {
  margin-top: 1.25rem;
}

.about-intro {
  margin-top: 0;
  font-size: 1.02rem;
  line-height: 1.7;
  color: var(--text-main);
}

.about-card p {
  line-height: 1.6;
  color: var(--text-main);
}

.about-card strong {
  color: var(--text-heading);
}

.mail-link {
  display: inline-flex;
  align-items: center;
  justify-content: center;

  width: 22px;
  height: 22px;
  margin-left: 0.35rem;

  color: var(--text-muted);
  text-decoration: none;

  vertical-align: -0.2rem;
}

.mail-link:hover {
  color: var(--icon-hover);
}

.mail-link svg {
  width: 17px;
  height: 17px;
  pointer-events: none;
}

.mail-link:hover svg,
.mail-link:hover svg path {
  stroke: var(--icon-hover);
}

.citation-link {
  color: var(--accent);
  text-decoration: none;
  font-weight: 600;
}

.citation-link:hover {
  text-decoration: underline;
}

.reference-entry {
  font-size: 0.92rem;
  color: var(--text-muted);
}

.energy-note {
  margin-top: 1rem;
  padding: 1rem 1.25rem;

  border: 1px solid var(--border-soft);
  border-radius: 8px;

  background: var(--bg-panel-alt);
}

.energy-formula {
  text-align: center;

  margin-bottom: 0.75rem;

  color: var(--text-heading);
  font-family: "Times New Roman", Times, serif;
  font-size: 1.35rem;
  font-style: italic;
}

.energy-note p {
  margin: 0;

  color: var(--text-main);
  line-height: 1.6;
}

.energy-note .energy-note-title {
  margin: 0 0 0.75rem;
  color: var(--text-muted);
}