Notifications that pop up on your website are flash messages. The style of flash messages on your website are defined in the theme.scss file. To adjust the color of the text, border, and background of flash messages you'll need to create a custom theme and edit the theme.scss file. Color is defined using hex color codes. 

The area of the theme.scss file that defines how flash messages display is:

#flash {
.notice {
padding: 8px 14px;
margin-bottom: 20px;
background-color: #fcf8e3;
@include border-radius(2px);
}
.flash-message {
display: inline-block;
}
button.flash-close {
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
font-size: 30px;
font-weight: bold;
line-height: 25px;
padding: 0;
margin: 0;
float: right;
color: #984949;
cursor: pointer;
border: 0;
background: transparent;
-webkit-appearance: none;
&:hover {
cursor: pointer;
}
}
.success {
background-color: #dff0d8;
border-color: #d6e9c6;
color: #468847;
}
.error {
background-color: #ead2d3;
border-color: #eed3d7;
color: #984949;
}
.info {
background-color: #d9edf7;
color: #3a87ad;
}
}

If you'd like to change the copy displayed in flash messages, you'll need to use Liquid filter statements in other theme files. 

You can remove the social sharing prompt from displaying on a page by editing the page and going to Settings > Social media and unchecking the box next to "Prompt for posting."