Header image not showing

I am using the sandbox theme to create a new blog. It’s at https://www.workshops-for-schools.co.uk/blog. I have used the same theme for my existing blog https://www.jollygoodfun.co.uk/blog. The header image on my exising blog works fine. I used the same code for my new blog and no matter what I do I can’t get it to work. I’ve tried changing the mark up, moving things around, using different images but still nothing. I’m baffled. I’ve even tried copying and pasting the code from my existing blog to the new one and it still won’t work. I’ve uploaded the header image to the correct folder on my server so it’s not that either.

Here is the code I’m using :

div#header{text-align:center;margin-bottom:1em; padding-top:6.5em;height: 120px;background:#FFFFFF url(‘images/wksbloghead.jpg’) no-repeat left;}
div#header h1{font-size: 36px;text-decoration: none; color:#CC0066;font-weight:bold;letter-spacing:-2px;line-height:36px;margin:0 5px 0 0; }
div#header h1 a{font-size: 36px;text-decoration: none;color: #993300;font-weight:bold;letter-spacing:-2px;line-height:24px;margin:0 5px 0 0;}
#header h1 a:hover{color:#3333FF;}
div#header div#blog-description{font-size:24px;color:#000000;font-weight: normal;letter-spacing:-2px;line-height:36px; }

This is the code from my existing site:

div#header{text-align:center;margin-bottom:1em; padding-top:6.5em;height: 120px;background:#FFFFFF url(‘images/blogheadjgp.jpg’) no-repeat left;}
div#header h1{font-size: 36px;text-decoration: none;color: #FF0000;font-weight:bold;letter-spacing:-2px;line-height:36px;margin:0 5px 0 0; }
div#header h1 a{font-size: 36px;text-decoration: none;color: #FF0000;font-weight:bold;letter-spacing:-2px;line-height:24px;margin:0 5px 0 0;}
#header h1 a:hover{color:#3333FF;}
div#header div#blog-description{font-size:24px;color:#000000;font-weight: normal;letter-spacing:-2px;line-height:36px; }

The image I’m using on both is 850 x 120px but I’ve tried other sizes too and it doesn’t have any effect.

Anyone got any ideas? I am stumped!