:root {
  --primary-color: #2563eb;
  --bg-color: #f3f4f6;
  --chat-bg: #ffffff;
  --user-bubble: #2563eb;
  --bot-bubble: #ffffff;
  --text-main: #1f2937;
  --text-muted: #6b7280;
  --border-color: #dbe2ea;
  --accent-light: #eff6ff;
  --input-bg: #ffffff;
  --valid-color: #10b981;
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

body {
  font-family: "Inter", "Segoe UI", Tahoma, sans-serif;
  background: linear-gradient(135deg, var(--bg-color) 0%, var(--accent-light) 100%);
  background-attachment: fixed;
  color: var(--text-main);
  margin: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  min-height: 100vh;
  padding: 12px;
  transition: background-color 0.3s ease, color 0.3s ease;
}

body.dark-mode {
  --bg-color: #111827;
  --chat-bg: #1f2937;
  --bot-bubble: #374151;
  --text-main: #f9fafb;
  --text-muted: #9ca3af;
  --border-color: #4b5563;
  --accent-light: #1e293b;
  --input-bg: #374151;
  --user-bubble: #2563eb;
  --valid-color: #34d399;
}

::selection {
  background: rgba(37, 99, 235, 0.2);
}

::-webkit-scrollbar {
  width: 8px;
  height: 8px;
}

::-webkit-scrollbar-track {
  background: transparent;
}

::-webkit-scrollbar-thumb {
  background: var(--border-color);
  border-radius: 999px;
}

::-webkit-scrollbar-thumb:hover {
  background: var(--text-muted);
}

#description {
  width: 100%;
  max-width: 720px;
  text-align: center;
  margin: 10px 0 18px;
  padding: 0 12px;
}

#description h1 {
  margin: 0 0 8px;
  font-size: clamp(1.4rem, 4.5vw, 2.1rem);
  line-height: 1.1;
  font-weight: 800;
}

.subtitle {
  margin: 0;
  color: var(--text-muted);
  font-size: clamp(0.92rem, 3vw, 1.02rem);
  line-height: 1.55;
}

#theme-toggle {
  position: fixed;
  top: 12px;
  left: 12px;
  width: 44px;
  height: 44px;
  border-radius: 999px;
  border: 1px solid var(--border-color);
  background: var(--chat-bg);
  color: var(--text-main);
  display: grid;
  place-items: center;
  font-size: 1.1rem;
  cursor: pointer;
  z-index: 1000;
  box-shadow: 0 6px 20px rgba(15, 23, 42, 0.08);
  transition: transform 0.15s ease, box-shadow 0.2s ease, background-color 0.2s ease;
}

#theme-toggle:hover,
button:hover {
  transform: translateY(-1px);
}

#theme-toggle:focus-visible,
button:focus-visible,
input:focus-visible,
a:focus-visible {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

#chat-container {
  width: min(100%, 820px);
  display: flex;
  flex-direction: column;
  border: 1px solid var(--border-color);
  border-radius: 22px;
  overflow: hidden;
  background: var(--chat-bg);
  box-shadow: 0 20px 40px rgba(15, 23, 42, 0.12);
  min-height: 500px;
  max-height: min(76vh, 760px);
}

.example-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 8px;
  padding: 12px 16px 0;
}

.example-label {
  font-size: 0.8rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--text-muted);
  margin-right: 4px;
}

.example-chip {
  border: 1px solid var(--border-color);
  background: linear-gradient(135deg, var(--accent-light), var(--chat-bg));
  color: var(--text-main);
  border-radius: 999px;
  padding: 8px 12px;
  font-size: 0.85rem;
  font-weight: 700;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}

.example-chip:hover {
  border-color: var(--primary-color);
  box-shadow: 0 8px 18px rgba(37, 99, 235, 0.12);
}

.example-chip:focus-visible {
  outline: 3px solid rgba(37, 99, 235, 0.35);
  outline-offset: 2px;
}

#chat-history {
  flex: 1;
  overflow-y: auto;
  padding: 16px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  background: rgba(0, 0, 0, 0.015);
}

.message-wrapper {
  display: flex;
  gap: 12px;
  max-width: min(92%, 720px);
  animation: messageSlide 0.25s ease-out;
}

.message-wrapper.user {
  align-self: flex-end;
  flex-direction: row-reverse;
}

.message-wrapper.bot {
  align-self: flex-start;
  width: 100%;
}

.avatar {
  width: 34px;
  height: 34px;
  border-radius: 10px;
  display: grid;
  place-items: center;
  flex-shrink: 0;
  font-weight: 700;
}

.bot-avatar {
  background: var(--primary-color);
  color: #fff;
}

.user-avatar {
  background: #475569;
  color: #fff;
}

.message {
  position: relative;
  padding: 12px 16px;
  border-radius: 18px;
  line-height: 1.6;
  word-break: break-word;
  white-space: pre-wrap;
}

.user-message {
  background: var(--user-bubble);
  color: #fff;
  border-bottom-right-radius: 6px;
}

.bot-message {
  background: var(--bot-bubble);
  color: var(--text-main);
  border: 1px solid var(--border-color);
  border-bottom-left-radius: 6px;
  box-shadow: 0 2px 8px rgba(15, 23, 42, 0.04);
}

.copy-proof-btn {
  position: absolute;
  top: 8px;
  right: 8px;
  width: 32px;
  height: 32px;
  border-radius: 8px;
  border: 1px solid var(--border-color);
  background: var(--accent-light);
  color: var(--text-muted);
  display: grid;
  place-items: center;
  opacity: 0;
  pointer-events: none;
}

.bot-message:hover .copy-proof-btn,
.copy-proof-btn:focus-visible {
  opacity: 1;
  pointer-events: auto;
}

.processing-container {
  padding: 4px 0;
}

.lvl-bar-bg {
  width: 100%;
  height: 6px;
  margin: 10px 0 8px;
  border-radius: 999px;
  background: #e5e7eb;
  overflow: hidden;
}

.lvl-bar-fill {
  width: 0%;
  height: 100%;
  background: var(--primary-color);
  transition: width 0.45s ease;
}

.status-text {
  font-size: 0.82rem;
  color: var(--text-muted);
  font-weight: 600;
}

.status-valid,
.status-invalid {
  font-size: 1rem;
  font-weight: 800;
  margin-bottom: 6px;
}

.status-valid {
  color: var(--valid-color);
}

.status-invalid {
  color: #ef4444;
}

.threat-box {
  border: 1px solid rgba(239, 68, 68, 0.25);
  border-left: 6px solid #ef4444;
  border-radius: 12px;
  background: linear-gradient(135deg, rgba(127, 29, 29, 0.12), rgba(239, 68, 68, 0.08));
  padding: 16px 18px;
  color: var(--text-main);
  box-shadow: 0 12px 28px rgba(127, 29, 29, 0.12);
}

.threat-title {
  color: #ef4444;
  font-size: 1.05rem;
  font-weight: 900;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  margin-bottom: 8px;
}

.threat-message {
  font-size: 1.05rem;
  font-weight: 700;
  line-height: 1.5;
}

.success-message {
  color: var(--valid-color);
  font-size: 1.08rem;
  font-weight: 700;
  margin-bottom: 8px;
}

.logic-header {
  font-size: 0.86rem;
  color: var(--text-muted);
  font-weight: 600;
  padding-bottom: 6px;
  margin-bottom: 8px;
  border-bottom: 1px solid var(--border-color);
}

.info-box {
  background: var(--accent-light);
  border: 1px solid var(--border-color);
  border-radius: 10px;
  padding: 10px 12px;
  margin: 10px 0;
  font-family: "Courier New", Courier, monospace;
  font-size: 0.85rem;
  overflow-x: auto;
}

.proof-container {
  margin-top: 8px;
}

.proof-empty {
  margin-top: 8px;
  padding: 8px 10px;
  border-radius: 10px;
  border: 1px dashed var(--border-color);
  color: var(--text-muted);
  font-size: 0.85rem;
  font-style: italic;
}

.proof-step {
  display: flex;
  align-items: baseline;
  gap: 8px;
  padding: 4px 0;
  font-family: "Courier New", Courier, monospace;
  font-size: 0.86rem;
}

.step-num {
  min-width: 28px;
  color: var(--text-muted);
  font-weight: 700;
}

.step-statement {
  flex: 1;
  color: var(--text-main);
  font-weight: 500;
}

.step-rule {
  color: var(--text-muted);
  white-space: nowrap;
  font-style: italic;
}

.reason-box {
  margin-top: 10px;
  padding: 10px 12px;
  border-left: 4px solid #ef4444;
  border-radius: 6px;
  background: rgba(239, 68, 68, 0.08);
  color: var(--text-main);
  font-size: 0.9rem;
}

.error-message {
  margin-top: 8px;
  color: var(--text-muted);
  font-size: 0.92rem;
}

#chat-container-footer {
  border-top: 1px solid rgba(0, 0, 0, 0.05);
  background: var(--chat-bg);
  box-shadow: 0 -4px 15px rgba(15, 23, 42, 0.03);
}

#chat-form {
  padding: 12px;
  display: flex;
  flex-direction: column;
  gap: 10px;
}

#symbol-bar {
  display: flex;
  gap: 8px;
  overflow-x: auto;
  padding-bottom: 4px;
}

#symbol-bar button {
  flex-shrink: 0;
  min-width: 44px;
  min-height: 40px;
  border-radius: 10px;
  border: 1px solid var(--border-color);
  background: var(--bg-color);
  color: var(--text-main);
  padding: 8px 12px;
  font-size: 1rem;
}

.input-wrapper {
  display: flex;
  gap: 10px;
  width: 100%;
}

#user-input {
  flex: 1;
  min-width: 0;
  border: 2px solid transparent;
  border-radius: 999px;
  background: var(--input-bg);
  color: var(--text-main);
  padding: 12px 16px;
  font-size: 0.98rem;
  transition: border-color 0.2s ease, box-shadow 0.2s ease, background-color 0.2s ease;
}

#user-input::placeholder {
  color: var(--text-muted);
}

#user-input:focus {
  border-color: var(--primary-color);
  box-shadow: 0 0 0 4px rgba(37, 99, 235, 0.12);
}

button {
  border: none;
  border-radius: 999px;
  background: var(--primary-color);
  color: #fff;
  padding: 12px 18px;
  font-weight: 700;
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.2s ease, opacity 0.2s ease;
}

button:active {
  transform: scale(0.97);
}

button:hover {
  box-shadow: 0 10px 24px rgba(37, 99, 235, 0.2);
}

footer {
  margin: 18px 0 8px;
  text-align: center;
  color: var(--text-muted);
  font-size: 0.9rem;
  line-height: 1.7;
  padding: 0 10px 8px;
}

footer a {
  color: var(--primary-color);
  text-decoration: none;
  font-weight: 700;
}

footer a:hover {
  text-decoration: underline;
}

.info-btn {
  margin-top: 10px;
  background: var(--primary-color);
}

.welcome-btn {
  width: 100%;
  margin-top: 12px;
}

#learnMoreBtn {
  width: 100%;
  margin-top: 8px;
  background: transparent;
  color: var(--primary-color);
  border: 1px solid var(--primary-color);
}

.welcome-modal,
.modal {
  position: fixed;
  inset: 0;
  z-index: 2000;
  background: rgba(0, 0, 0, 0.5);
  backdrop-filter: blur(4px);
}

.welcome-modal {
  display: flex;
  align-items: center;
  justify-content: center;
}

.modal {
  display: none;
}

.welcome-content,
.modal-content {
  width: min(92vw, 700px);
  max-height: 90vh;
  overflow-y: auto;
  border-radius: 18px;
  border: 1px solid var(--border-color);
  background: var(--chat-bg);
  box-shadow: 0 18px 40px rgba(15, 23, 42, 0.28);
  padding: 22px;
  animation: modalSlideUp 0.25s ease-out;
}

.welcome-content {
  width: min(92vw, 620px);
  text-align: center;
}

.welcome-header h1,
.modal-header h2 {
  margin: 0;
}

.welcome-header p {
  margin: 8px 0 0;
  color: var(--text-muted);
  line-height: 1.5;
}

.welcome-features {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 12px;
  margin: 18px 0;
  text-align: left;
}

.feature-item {
  background: var(--accent-light);
  border-left: 4px solid var(--primary-color);
  border-radius: 10px;
  padding: 12px;
}

.feature-item strong {
  display: block;
  margin-bottom: 5px;
  color: var(--primary-color);
}

.feature-item p {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.9rem;
  line-height: 1.45;
}

.welcome-copy,
.pro-tips {
  color: var(--text-muted);
  line-height: 1.6;
  margin: 10px 0 0;
}

.modal-content {
  margin: 5vh auto;
}

.modal-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  border-bottom: 1px solid var(--border-color);
  padding-bottom: 10px;
  margin-bottom: 12px;
}

.close-btn {
  width: 36px;
  height: 36px;
  background: transparent;
  color: var(--text-muted);
  font-size: 1.5rem;
  line-height: 1;
  padding: 0;
}

.modal-body {
  color: var(--text-main);
  font-size: 0.96rem;
  line-height: 1.65;
}

.modal-body hr {
  border: 0;
  height: 1px;
  background: var(--border-color);
  margin: 14px 0;
}

.modal-body h3 {
  color: var(--primary-color);
  margin: 0 0 8px;
}

.modal-body ul {
  margin: 0;
  padding-left: 20px;
}

.modal-body li {
  margin: 6px 0;
}

.modal-example-box {
  border-left: 4px solid var(--primary-color);
  border-radius: 10px;
  padding: 12px;
  margin: 14px 0;
  background: var(--accent-light);
}

.modal-example-box strong {
  display: block;
  margin-bottom: 8px;
}

.modal-example-box pre {
  margin: 0;
  white-space: pre-wrap;
  word-break: break-word;
  font-family: "Courier New", Courier, monospace;
  font-size: 0.92rem;
}

.valid-example {
  background: rgba(16, 185, 129, 0.08);
  border-left-color: #10b981;
}

.invalid-example {
  background: rgba(239, 68, 68, 0.08);
  border-left-color: #ef4444;
}

@keyframes messageSlide {
  from {
    opacity: 0;
    transform: translateY(12px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes modalSlideUp {
  from {
    opacity: 0;
    transform: translateY(24px);
  }
  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (max-width: 768px) {
  body {
    padding: 10px;
  }

  #theme-toggle {
    width: 42px;
    height: 42px;
  }

  #chat-container {
    width: 100%;
    min-height: 0;
    max-height: 76vh;
  }

  .welcome-features {
    grid-template-columns: 1fr;
  }

  .input-wrapper {
    flex-direction: column;
  }

  .input-wrapper button {
    width: 100%;
  }

  .message-wrapper {
    max-width: 96%;
  }

  .modal-content,
  .welcome-content {
    width: 100%;
    border-radius: 18px 18px 0 0;
    margin: 0;
    max-height: 92vh;
  }

  .welcome-modal,
  .modal {
    align-items: flex-end;
  }
}