Website not loading correctly on tablet or mobile

Good Afternoon

Can you please help with the following on my website http://www.thedogsclub.com

On a desktop/laptop the site looks fine, however on a 7 inch tablet the righthand side is not so good. At the top right the Login/Register words are in the correct place but the clickable behind the words and in the wrong place.
I was told to add the following code into the Custom CSS, but the problem is still there.
body > div.container_24.container > div.grid_24.header > div:nth-child(1) {
max-width: 100%;
}
.header img {
max-width: 100%;
}

Also on the footer widget for Twitter using a tablet or mobile there is a black box over the rolling text which is not there on a laptop.

I am trying to launch my new site but no one can register at the moment.

On a standard size mobile phone it is the same problem but worse.

Many thanks
Yvonne