svg

draw a rect

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<rect width='300' height='100' fill='red' stroke-width='3' stroke='green'/><
</svg>

or like this

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
"http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">

<rect width='300' height='100' style='fill:red;stroke-width:3;stroke:green'/>

</svg>

draw a circle

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<circle cx='50' cy='50' r='30' stroke='green' stroke-width='4' fill='red'/>
</svg>

image.png

draw a line

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<line x1='0' y1='0' x2='40' y2='40' stroke='green' stroke-width='3' fill='red'/>
</svg>

draw a polygon

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<polygon points='10,20 50,100 60,300' stroke='green' stroke-width='3' fill='red'/>
</svg>

image.png

draw a polyline

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<polyline points='10,20 50,100 60,300 ' stroke='green' stroke-width='3' fill='white'/>
</svg>

image.png

linearGradient

<svg width="100%" height="100%" version="1.1"
xmlns="http://www.w3.org/2000/svg">
<defs>
<linearGradient id='jb' y1='0%' y2='0%' x1='0%' x2='100%'>
<stop offset='0%' stop-color='yellow'></stop>
<stop offset='100' stop-color='red'></stop>
    
</linearGradient>
</defs>
<rect width='300' height='100' fill='url(#jb)'/>
</svg>

image.png

ref

如何给SVG填充和描边应用线性渐变 - 看不懂。。 - 博客园