:root {
  --binder-bg: #ab8d6f; /* Cardboard */
  --paper-white: #fafafa;
  --blue-rule: #a5c3ff;
  --margin-red: #ff8b8b;
  --text-ink: #1e1e24;
  
  --font-hand: 'Architects Daughter', cursive;
}

body {
  margin: 0;
  padding: 0;
  background-color: var(--binder-bg);
  background-image: radial-gradient(rgba(0,0,0,0.15) 12%, transparent 13%);
  background-size: 16px 16px;
  color: var(--text-ink);
  font-family: var(--font-hand);
  line-height: 24px; /* Matches ruled lines */
}

.notebook-container {
  max-width: 950px;
  margin: 0 auto;
  padding: 60px 20px;
}

.notebook-header {
  text-align: center;
  margin-bottom: 50px;
}

.nav-back {
  display: inline-block;
  color: var(--text-ink);
  text-decoration: underline;
  margin-bottom: 20px;
  font-weight: bold;
}

.notebook-title {
  font-size: clamp(2.5rem, 5vw, 3.8rem);
  margin: 0 0 10px 0;
}

.notebook-subtitle {
  margin: 0;
  opacity: 0.8;
}

.notebook-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(290px, 1fr));
  gap: 35px;
}

/* Lined Binder Paper sheet */
.paper-sheet {
  background-color: var(--paper-white);
  /* 24px lines repeating */
  background-image: linear-gradient(var(--blue-rule) 1px, transparent 1px);
  background-size: 100% 24px;
  border-radius: 4px;
  box-shadow: 0 15px 30px rgba(0, 0, 0, 0.3);
  padding: 30px 30px 30px 55px; /* Offset for spiral spine */
  position: relative;
  min-height: 240px;
  box-sizing: border-box;
  transition: transform 0.3s;
}

.paper-sheet:hover {
  transform: translateY(-4px);
}

/* Ruled Red Margin */
.red-margin {
  position: absolute;
  top: 0;
  left: 45px;
  width: 1px;
  height: 100%;
  border-left: 1.5px solid var(--margin-red);
}

/* Repeating Spiral spine rings */
.spiral-spine {
  position: absolute;
  top: 0;
  left: 10px;
  width: 25px;
  height: 100%;
  background-image: 
    radial-gradient(#444 35%, transparent 35%),
    linear-gradient(90deg, #999, #bbb 40%, #555 70%, #999 100%);
  background-size: 10px 24px, 4px 100%;
  background-repeat: repeat-y, no-repeat;
  background-position: center top, 5px center;
  border-right: 1.5px dashed #ccc;
  opacity: 0.85;
}

.paper-sheet h2 {
  font-size: 1.45rem;
  margin-top: 0;
  margin-bottom: 24px;
}

.paper-sheet p {
  margin: 0 0 24px 0;
  font-size: 0.95rem;
}

/* Drawing sketchpad */
.sketch-wrapper {
  border: 1px solid #ddd;
  background-color: #fff;
  box-shadow: inset 0 2px 4px rgba(0,0,0,0.05);
}

#sketch-canvas {
  width: 100%;
  cursor: pointer;
  display: block;
}

.sketch-btn {
  background: transparent;
  border: 1.5px dashed var(--text-ink);
  color: var(--text-ink);
  font-family: inherit;
  font-size: 0.85rem;
  padding: 6px 12px;
  margin-top: 15px;
  cursor: pointer;
}

.sketch-btn:hover {
  background: rgba(0, 0, 0, 0.05);
}

/* List checkbox */
.task-list {
  list-style: none;
  padding-left: 0;
  margin: 0;
}

.task-list li {
  margin-bottom: 0px; /* spacing fits lined height */
}