sass-mixins-plain-css.css

.container {
  width: 960px;
  margin: 0 auto;
  border: 1px solid navy;
  padding: 15px 15px 15px 15px;
  color: #333333;
}
.container h1 {
  text-align: center;
  border: 1px solid navy;
  -webkit-border-radius: 20px;
  -moz-border-radius: 20px;
  -o-border-radius: 20px;
  -ms-border-radius: 20px;
  border-radius: 20px;
  font-size: 54px;
  color: navy;
}
.container h2 {
  font-size: 36px;
}
.container h2 span {
  font-style: italic;
}
.container h2 span:before {
  content: '- ';
}
.container h2:after {
  content: " with Sass";
}
.container #mypara {
  color: navy;
}

.footer {
  text-align: center;
  border: 1px solid navy;
  -webkit-border-radius: 20px;
  -moz-border-radius: 20px;
  -o-border-radius: 20px;
  -ms-border-radius: 20px;
  border-radius: 20px;
}
.footer p {
  font-size: 18px;
}

sass-mixins.html

<div class='container'>

  <h1>SASS - Mixins</h1>
  <h2><span>Basic</span> - Getting Started</h2>

  <p id='mypara'>Lorem ipsum dolor sit amet, consectetur
  adipiscing elit, sed do eiusmod tempor <br>
  incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
  nostrud exercitation ullamco laboris nisi</p>
  
  <p>Lorem ipsum dolor sit amet, consectetur
  adipiscing elit, sed do eiusmod tempor
  incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis
  nostrud exercitation ullamco laboris nisi</p>

  <div class='footer'>
    <p>/&copy; Copyright<p>
  </div>

</div><!--container-->

sass-mixins.scss

// ----
// Sass (v3.4.7)
// Compass (v1.0.1)
// ----

$Color1: navy;                            // named color value
$Color2: #333333;                         // hex color value
$StringVar: " with Sass";                 // string variable 
$FontSize: 18px;                          // numeric value
$border: 1px solid $Color1;              // multi-value variable
$padding: 15px 15px 15px 15px;           // multi-value variable

@mixin radius ($radius) {
  -webkit-border-radius:$radius;
 -moz-border-radius: $radius;
 -o-border-radius: $radius;
 -ms-border-radius: $radius;
 border-radius: $radius;
}

@mixin default{
  text-align: center;
  border: $border;
  @include radius(20px);
}


.container {
   width: 960px;
   margin: 0 auto;
   border: $border;
   padding: $padding;
   color: $Color2;
   
   h1 {
    @include default;
    font-size: $FontSize*3;
    color: $Color1;

   }
   
   h2 {
    font-size: $FontSize*2; 
    span {
      font-style: italic;
       &:before {
         content: '- ';
       }
    }
     &:after {
       content: $StringVar;
     }
   }
   
   #mypara {
     color: $Color1;
   }
}

.footer {
  @include default;
  p {
    font-size: $FontSize;
  }
}