static/style.css

/*
  style.css — GPT-2 Playground
  ==============================
  Design tokens and component styles for the generation interface.

  Color system
  ------------
  --bg-*          dark indigo backgrounds (darkest → surface)
  --purple-*      purple scale (accent, hover states)
  --blue-*        blue scale (gradient pair)
  --text-*        foreground hierarchy
  --border        subtle separator

  Component hierarchy
  -------------------
  site-header
  main-layout
    controls-panel   (parameter sliders)
    generation-panel (textarea, output pane)
*/

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg-base:        #0b0718;
  --bg-surface:     #13102b;
  --bg-raised:      #1c1840;
  --bg-input:       #0f0c24;

  --purple-400: #84d2fc;
  --purple-500: #5588f7;
  --purple-600:     #9333ea;
  --purple-700:     #7c3aed;

  --blue-500:       #3b82f6;
  --blue-600:       #2563eb;

  --grad-primary:   linear-gradient(135deg, #0054fd 0%, #2563eb 100%);
  --grad-shimmer:   linear-gradient(90deg, #2d31ff, #1068ea, #2563eb, #4f46e5, #7c3aed);

  --text-primary:   #ede9fe;
  --text-secondary: #8ba5fa;
  --text-muted: #5f68a6;
  --text-on-grad:   #ffffff;

  --border: rgba(1, 189, 255, 0.25);
  --border-focus: rgba(85, 136, 247, 0.6);

  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 16px;

  --font-display: "Space Grotesk", sans-serif;
  --font-body:    "Inter", sans-serif;
  --font-mono:    "JetBrains Mono", monospace;
}

html, body {
  height: 100%;
  background-color: var(--bg-base);
  color: var(--text-primary);
  font-family: var(--font-body);
  font-size: 14px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

/* ── Accessibility ── */
.sr-only {
  position: absolute; width: 1px; height: 1px;
  padding: 0; margin: -1px; overflow: hidden;
  clip: rect(0,0,0,0); white-space: nowrap; border: 0;
}

/* ── Background ambient glow ── */
body::before {
  content: "";
  position: fixed; inset: 0; pointer-events: none; z-index: 0;
  background:
    radial-gradient(ellipse 60% 40% at 20% 10%, rgba(124,58,237,0.18) 0%, transparent 70%),
    radial-gradient(ellipse 50% 35% at 80% 80%, rgba(37,99,235,0.14) 0%, transparent 70%);
}

/* ── Header ── */
.site-header {
  position: relative; z-index: 10;
  display: flex; align-items: center; justify-content: space-between;
  padding: 16px 32px;
  border-bottom: 1px solid var(--border);
  background: rgba(11, 7, 24, 0.8);
  backdrop-filter: blur(12px);
}

.logo {
  display: flex; align-items: center; gap: 10px;
  font-family: var(--font-display);
  font-size: 17px; font-weight: 600;
  color: var(--text-primary);
}

.model-badge {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--purple-400);
  background: rgba(124, 58, 237, 0.15);
  border: 1px solid rgba(124, 58, 237, 0.3);
  padding: 4px 10px;
  border-radius: 100px;
  letter-spacing: 0.02em;
}

/* ── Layout ── */
.main-layout {
  position: relative; z-index: 1;
  display: grid;
  grid-template-columns: 280px 1fr;
  gap: 24px;
  max-width: 1100px;
  margin: 0 auto;
  padding: 32px 24px 48px;
  min-height: calc(100vh - 65px);
  align-items: start;
}

/* ── Controls panel ── */
.controls-panel {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 24px;
  position: sticky;
  top: 24px;
}

.panel-title {
  font-family: var(--font-display);
  font-size: 13px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-secondary);
  margin-bottom: 20px;
}

.control-group {
  margin-bottom: 22px;
}

.control-group label {
  display: flex;
  justify-content: space-between;
  align-items: center;
  font-size: 13px;
  font-weight: 500;
  color: var(--text-primary);
  margin-bottom: 8px;
}

.value-display {
  font-family: var(--font-mono);
  font-size: 12px;
  color: var(--purple-400);
  background: rgba(85, 123, 247, 0.12);
  padding: 2px 7px;
  border-radius: 4px;
  min-width: 38px;
  text-align: center;
}

/* Custom range slider */
input[type="range"] {
  -webkit-appearance: none;
  width: 100%;
  height: 4px;
  background: var(--bg-raised);
  border-radius: 2px;
  outline: none;
  cursor: pointer;
}

input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 16px; height: 16px;
  border-radius: 50%;
  background: var(--grad-primary);
  background: linear-gradient(135deg, var(--purple-500), var(--blue-500));
  box-shadow: 0 0 0 3px rgba(0, 31, 255, 0.2);
  transition: box-shadow 0.2s;
}

input[type="range"]::-webkit-slider-thumb:hover {
  box-shadow: 0 0 0 5px rgba(85, 131, 247, 0.3);
}

input[type="range"]::-moz-range-thumb {
  width: 16px; height: 16px;
  border: none; border-radius: 50%;
  background: linear-gradient(135deg, var(--purple-500), var(--blue-500));
}

.param-explainer {
  margin-top: 24px;
  padding-top: 18px;
  border-top: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.param-explainer p {
  font-size: 12px;
  color: var(--text-muted);
  line-height: 1.5;
}

.param-explainer strong {
  color: var(--text-secondary);
  font-weight: 500;
}

/* ── Generation panel ── */
.generation-panel {
  display: flex;
  flex-direction: column;
  gap: 20px;
}

/* Prompt textarea */
.prompt-area {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
  transition: border-color 0.2s;
}

.prompt-area:focus-within {
  border-color: var(--border-focus);
  box-shadow: 0 0 0 3px rgba(85, 98, 247, 0.1);
}

#promptInput {
  width: 100%;
  background: transparent;
  border: none;
  outline: none;
  resize: none;
  padding: 18px 20px 12px;
  font-family: var(--font-body);
  font-size: 15px;
  color: var(--text-primary);
  line-height: 1.65;
  caret-color: var(--purple-400);
}

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

.prompt-footer {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 16px 14px;
  border-top: 1px solid var(--border);
}

.char-count {
  font-family: var(--font-mono);
  font-size: 11px;
  color: var(--text-muted);
}

/* Generate button */
.btn-generate {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 9px 22px;
  background: var(--grad-primary);
  color: var(--text-on-grad);
  font-family: var(--font-display);
  font-size: 14px;
  font-weight: 600;
  border: none;
  border-radius: var(--radius-md);
  cursor: pointer;
  position: relative;
  overflow: hidden;
  transition: opacity 0.15s, transform 0.1s;
}

.btn-generate:hover:not(:disabled) {
  opacity: 0.92;
  transform: translateY(-1px);
}

.btn-generate:active:not(:disabled) {
  transform: translateY(0);
}

.btn-generate:disabled {
  cursor: not-allowed;
  opacity: 0.7;
}

/* Shimmer animation while generating */
.btn-generate.is-loading {
  background-size: 300% 100%;
  animation: shimmerBg 1.5s linear infinite;
}

@keyframes shimmerBg {
  0%   { background-position: 100% 50%; }
  100% { background-position:   0% 50%; }
}

.btn-generate.is-loading .btn-label { opacity: 0; }
.btn-generate .btn-spinner { display: none; }

.btn-generate.is-loading .btn-spinner {
  display: block;
  position: absolute;
  inset: 0; margin: auto;
  width: 18px; height: 18px;
  border: 2px solid rgba(255,255,255,0.3);
  border-top-color: white;
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* ── Output pane ── */
.output-container {
  background: var(--bg-surface);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  overflow: hidden;
}

.output-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 16px;
  border-bottom: 1px solid var(--border);
  background: var(--bg-raised);
}

.output-label {
  font-family: var(--font-display);
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--text-secondary);
}

.btn-copy {
  display: inline-flex; align-items: center; gap: 5px;
  padding: 4px 10px;
  background: transparent;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  color: var(--text-muted);
  font-size: 12px;
  cursor: pointer;
  transition: color 0.15s, border-color 0.15s, background 0.15s;
}

.btn-copy:hover:not(:disabled) {
  color: var(--text-primary);
  border-color: var(--purple-600);
  background: rgba(124, 58, 237, 0.12);
}

.btn-copy:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.btn-copy.copied {
  color: #34d399;
  border-color: rgba(52, 211, 153, 0.4);
}

.output-body {
  padding: 20px;
  min-height: 180px;
  font-family: var(--font-mono);
  font-size: 13.5px;
  line-height: 1.75;
}

.output-prompt {
  color: var(--text-muted);
  white-space: pre-wrap;
  word-break: break-word;
}

.output-prompt:not(:empty)::after {
  content: "";
  display: inline-block;
  width: 0;
}

.output-generated {
  color: var(--text-primary);
  white-space: pre-wrap;
  word-break: break-word;
}

.output-prompt:not(:empty) + .output-generated {
  border-left: 2px solid var(--purple-700);
  padding-left: 12px;
  margin-top: 12px;
  color: var(--text-primary);
}

.placeholder-text {
  color: var(--text-muted);
  font-family: var(--font-body);
  font-size: 13px;
  font-style: italic;
}

/* ── Error banner ── */
.error-banner {
  padding: 12px 16px;
  background: rgba(220, 38, 38, 0.12);
  border: 1px solid rgba(220, 38, 38, 0.35);
  border-radius: var(--radius-md);
  color: #fca5a5;
  font-size: 13px;
}

/* ── Responsive ── */
@media (max-width: 768px) {
  .main-layout {
    grid-template-columns: 1fr;
    padding: 20px 16px 40px;
  }

  .controls-panel {
    position: static;
  }

  .site-header {
    padding: 14px 20px;
  }
}