CSS border in Chrome: strange grey line - css

Question

I have a problem with a border in Chrome. The green border has some grey lines.
Firefox: not visible -> ok!
Chrome: not visible but visible in the dev tools, mobile phone.
Chrome on my phone: visible
Here is a screenshot that shows my problems!
https://abload.de/img/cssiee7s.jpg
1) When you go to http://www.seelenpuls.at/hpneu/m_biografie_leander_de.php
there are two small grey lines
2) When you go to http://www.seelenpuls.at/hpneu/m_neues_de.php there are even more problems.
3) The menu button has an orange border (mobile only) ... and I don't know why as there is no such color in my CSS.
Please help!
Here's the code. The bold part is the border that causes the problems.
* { padding: 0; margin: 0; }
body
{
font-family: sans-serif, Verdana, Arial;
color: #000000;
background-color: #556B2F;
}
#center {
position: relative;
width: 350px;
height: 630px;
box-sizing: border-box;
margin: 5px auto 0px auto;
}
#logo {
position: absolute;
width: 350px;
height: 220px;
background-color: #ffffff;
box-sizing: border-box;
background-image: url("img/m_bg_c.jpg");
background-repeat: no-repeat;
background-size: 350px 220px;
}
#navi
{
position: absolute;
top: 175px;
width: 60px;
height: 40px;
font-size: 16px;
color: #000000;
background-color: #ffffff;
margin-left: 10px;
}
#header
{
position: absolute;
top: 187px;
width: 238px;
height: 30px;
font-size: 16px;
color: #000000;
left: 85px;
}
#content
{
position: absolute;
top: 218px;
width: 350px;
box-sizing: border-box;
color: #000000;
background-color: #ffffff;
font-size: 14px;
overflow: auto;
padding-left: 5px;
padding-right: 5px;
**border-bottom: 5px solid #556B2F**;
}

Answer 1

Ok so there is a couple of things that are going on in your css.
White lines
For your content div, I would use a width of 100% for mobile devices now, as you scale to tablets and desktops you can change to a more fixed or fluid width. I would also remove the border bottom property. This is not fully extending to the width of the content box and I am unsure if it has to do with the border-sizing property you are using. I would also apply the border-sizing this way so it is applied to every element in your html
* {
box-sizing: border-box;
}
Orange border - this is caused by the :focus pseudo css property of the button you are using, you can remove it this way
button:focus {
outline: none;
}
CSS Normalize or CSS Reset - consider using one of these stylesheets in your website. They help you rendering all elements more consistently through all browsers. This will save you the time of remove the :focus property, like I mentioned above in any project moving forward. Most popular CSS frameworks utilize this to normalize basic styles.
Link to Normalize.css