DotNet connection string fot SQL Server

App.config

<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <configSections>
    </configSections>
    <connectionStrings>
        <add name="Dolphin_Accounts.Properties.Settings.sql_connection"
            connectionString="Data Source=.\sqlexpress;Initial Catalog=dolphine;User ID=sa;Password=" />
    </connectionStrings>
    <startup> 
        <supportedRuntime version="v4.0" sku=".NETFramework,Version=v4.7.2"/>
    </startup>
  
</configuration>