Question: I have a data in following format:

```

ID  time0       obs_num recorded_dt 
1   2009-01-01  A       2009-01-01  
1   2009-01-01  D       2009-01-31  
1   2009-01-01  B       2009-01-05  
2   2005-02-02  B       2005-02-03  

```

I want to calculate columns based on days difference for up to a month in reference to time0 and add respective values from the obs\_num column. In the end, the data should look like this:

```

ID  time0       obs_num recorded_dt day0    day1    day2    day3    day4    day5    ... day31
1   2009-01-01  A       2009-01-01  A       NULL    NULL    NULL    NULL    NULL    ... NULL
1   2009-01-01  D       2009-01-31  NULL    NULL    NULL    NULL    NULL    NULL    ... D
1   2009-01-01  B       2009-01-05  NULL    NULL    NULL    NULL    NULL    B       ... NULL
2   2005-02-02  B       2005-02-03  NULL    B       NULL    NULL    NULL    NULL    ... NULL

```

Answer: 
```html
<header>
    <div class="logo">
        <a href=""><img src="Images/samsung-logo.png" alt="Samsung Logo" width="150"></a>
        <ul class="menubalk">
            <li><a href="#">Contact</a></li>
            <li><a href="#">Assortiment</a></li>
        </ul>
    </div>
</header>
<div class="bg">
   <video src="videos/S22-Ultra-unboxing.mp4" muted loop autoplay></video>
   <div class="bg-text">Nieuwe S22 Ultra</div>            
   <div class="bg-text-url"><a href="#">Discover</a></div>
</div>
```

Element `a` not allowed as child of element `ul` in this context.
Also when you using a `div` element `a` not allowed as a parent child.
The reason why your anchor tags are not working is a combination of using `display: inline;` styles and `position: absolute;`. To fix this issue, update your styles to be accurate to [this](https://jsfiddle.net/x7jnLpue/3/) JSFiddle. I have also corrected some of your syntax.