fill fill color, or you can write css to fill

one more line, path3, is between 1 and 2, and the code is as follows:

< svg width= "100%" height= "100%" >

<line x1="50" y1="75" x2="200" y2="75" style="stroke:red;stroke-width:2;"/>
<line x1="50" y1="100" x2="200" y2="100" style="stroke:blue;stroke-width:50;"/>
<line x1="50" y1="125" x2="200" y2="125" style="stroke:red;stroke-width:2;"/>

< / svg >