def line_height(style, name, value):
    """Compute the ``line-height`` property."""
    if value == 'normal':
        return value
    elif not value.unit:
        return ('NUMBER', value.value)
    elif value.unit == '%':
        factor = value.value / 100
        font_size_value = style['font_size']
        pixels = factor * font_size_value
    else:
        pixels = length(style, name, value, pixels_only=True)
    return ('PIXELS', pixels)
Compute the ``line-height`` property.
weasyprint/css/computed_values.py