Hi tasag,
If you want to display the product_code under the product_name, in HikaShop > Display > Views
Edit the view "show_default" (in the good template), add :
between the two span tags in the H1 tag.
Like that:
<h1>
<span id="hikashop_product_name_main" class="hikashop_product_name_main">
<?php
if (hikashop_getCID('product_id')!=$this->element->product_id && isset ($this->element->main->product_name))
echo $this->element->main->product_name;
else
echo $this->element->product_name;
?>
</span><br />
<span id="hikashop_product_code_main" class="hikashop_product_code_main">
<?php
echo $this->element->product_code;
?>
</span>
</h1>
For the CSS styling, you just have to edit the same CSS File as previous, and add for example:
.hikashop_product_code_main{
color: red;
size: 16px;
}