add(layout/Marging): relative margins for Elements

src/render.zig

@@ -131,6 +131,7 @@ pub fn Direct(comptime _: bool) type {
 
         pub fn clear(this: *@This(), size: Size) !void {
             _ = this;
+            // TODO: this should instead by dynamic and correct of size (terminal could be too large currently)
             std.debug.assert(1028 > size.cols);
             var buf: [1028]u8 = undefined;
             @memset(buf[0..], ' ');