The <linearGradient> tag is used to define SVG linear
The <linearGradient> tag must be nested within <defs>
tag. The <defs> tag is short for definition and it allows
definition of special elements such as gradients.
Linear gradients can be defined as vertical ,horizontal or
Vertical gradients are created when x1 and x2 are equal
and y1 and y2 are differed.
Horizontal gradients are created when y1 and y2 are
equal and x1 and x2 are differed.
Angular gradients are created when x1 and x2 differ and
y1 and y2 are differed.