#problem-prompt {
    text-align: center;
    font-size: 1.3rem;
    font-weight: 600;
    margin: 1.5rem 0 1rem;
    color: #333;
}

#conversion-chain {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    flex-wrap: wrap;
    margin: 1rem 0;
    padding: 1rem;
    background: #f8f9fa;
    border: 1px solid #dee2e6;
    border-radius: 12px;
    min-height: 90px;
}

#start-value {
    font-size: 1.3rem;
    font-weight: bold;
    color: #333;
}

#drop-zones {
    display: flex;
    align-items: center;
    gap: 6px;
    flex-wrap: wrap;
}

.drop-zone {
    min-width: 130px;
    min-height: 70px;
    padding: 6px 10px;
    border: 2px dashed #bbc8ca;
    border-radius: 8px;
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    font-size: 0.85rem;
    color: #adb5bd;
    cursor: pointer;
    transition: border-color 0.2s, background-color 0.2s;
}

.drop-zone:hover,
.drop-zone.drag-hover {
    border-color: #6153cc;
    background-color: #f0eeff;
}

.drop-zone.filled {
    border-style: solid;
    border-color: #6153cc;
    background: white;
    color: #333;
    cursor: pointer;
}

.drop-zone.correct {
    border-color: #28a745;
    background-color: #e6f9e8;
}

.drop-zone.incorrect {
    border-color: #dc3545;
    background-color: #fde8e8;
}

.multiply-sign {
    font-size: 1.2rem;
    color: #6c757d;
    font-weight: bold;
}

#equals-sign {
    font-size: 1.3rem;
    font-weight: bold;
    color: #495057;
}

#target-unit {
    font-size: 1.1rem;
    font-weight: 600;
    color: #6153cc;
}

#tile-tray {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 10px;
    margin: 1rem 0;
    padding: 1rem;
    min-height: 80px;
}

.factor-tile {
    display: flex;
    flex-direction: column;
    align-items: center;
    padding: 8px 16px;
    border: 2px solid #dee2e6;
    border-radius: 8px;
    background: white;
    cursor: pointer;
    transition: transform 0.15s, box-shadow 0.15s, border-color 0.15s;
    user-select: none;
    min-width: 100px;
}

.factor-tile:hover {
    border-color: #6153cc;
    transform: translateY(-2px);
    box-shadow: 0 2px 8px rgba(0,0,0,0.1);
}

.factor-tile.placed {
    opacity: 0.35;
    pointer-events: none;
}

.tile-numerator,
.drop-zone .tile-numerator {
    font-size: 0.95rem;
    font-weight: 600;
    padding-bottom: 4px;
    border-bottom: 2px solid #495057;
    width: 100%;
    text-align: center;
    white-space: nowrap;
}

.tile-denominator,
.drop-zone .tile-denominator {
    font-size: 0.95rem;
    font-weight: 600;
    padding-top: 4px;
    width: 100%;
    text-align: center;
    white-space: nowrap;
}

.unit-cancelled {
    text-decoration: line-through;
    color: #adb5bd;
}