fix(example/styles): provide necessary size for text display through the element

This could also be done through the `resize` function interface of the
`Element` or the corresponding `Container` from the outside (as done in
this example - as the size is know at compile-time).

examples/styles/text.zig

@@ -111,6 +111,12 @@ pub fn main() !void {
 
     var box = try App.Container.init(allocator, .{
         .layout = .{ .direction = .vertical },
+        .size = .{
+            .dim = .{
+                .x = std.meta.fields(zterm.Style.Emphasis).len * TextStyles.text.len,
+                .y = (std.meta.fields(zterm.Color).len - 1) * (std.meta.fields(zterm.Color).len - 2),
+            },
+        },
     }, text_styles.element());
     defer box.deinit();