Add Svg Render
div #block { background-color: #00000000; background-image: "$svg{iui_forge:textures/svg/test.svg, 100%, 100%}"; size: 20; }
or  或
div #block { background-color: #00000000; background-image: "$svg{iui_forge:textures/svg/test.svg, 100%}"; size: 20; }
or  或
div #block { background-color: #00000000; background-image: "$svg{iui_forge:textures/svg/test.svg}"; size: 20; }
If your .svg
is modified through the resource pack, the in-game rendering will change with F3 + T
.