Quick launch (Left navigation) styles in SharePoint 2013

Modify the master page

• Add a link to Custom Css in master page.
• On the head tag of master page html add below highlight lines

<!--SPM:<SharePoint:CssRegistration Name="Themable/corev15.css" runat="server"/>-->

<!--SPM:<SharePoint:CssRegistration Name="https://portal.sharepoint.com/Style Library/Master.css" runat="server" After="corev15.css" />-->

• In your Custom master.css file, add the below CSS classes

 .ms-core-listMenu-verticalBox UL.root > LI > .menu-item{  
  font-weight:bold;  
  background-color:#5482AB;  
  color:#ffffff;  
  border-bottom-color:#ffffff;  
  border-bottom-style:solid;  
  border-bottom-width:1px;  
  min-height:25px;  
  padding-top:5px;  
  padding-left:10px;  
  font-size:12px;  
  font-family:Arial, Helvetica, Sans-Serif !important;  
 }  
 .ms-core-listMenu-verticalBox > ul.root > li.static > ul.static > li.static > a:hover {  
   color: #ffffff !important;  
   background-color:#D95E00 !important;  
   text-decoration:none;  
 }  
 .ms-core-listMenu-verticalBox > ul.root > li.selected > a {  
    background-image:none;  
    background-color:#D95E00;  
   color:#ffffff !important;  
 }  
 .ms-core-listMenu-verticalBox > ul.root > li > a:hover {  
    background-image:none;  
    background-color:#D95E00;  
   color:#ffffff !important;  
   text-decoration:underline;  
 }  
 .ms-core-listMenu-verticalBox > ul.root > li.static > ul.static > li > a {  
  font-size:12px;  
  padding-left:10px;  
  font-family:Arial, Helvetica, Sans-Serif !important;  
 }  
 .ms-core-listMenu-verticalBox > ul.root > li.static > ul.static > li > a.selected {  
   background:none;  
    color: #D95E00 !important;  
   background-color:#ffffff !important;  
    text-decoration: none;  
    border: 1px #fff solid;  
    font-weight:bold;  
 }  
 .ms-core-listMenu-verticalBox a.selected  
 {  
  border: 1px #fff solid !important;  
 }  
 .ms-core-listMenu-verticalBox UL.root UL  
 {  
  margin:0px 0px 10px 0px !important;  
 }