页面无法加载CSS样式

写了一个简单的登录页面，可是为什么加载不了外部CSS样式呢？可有人知道原因？

程序代码：

package main

import (
    "fmt"
    "html/template"
    "net/http"
    "strings"
    "log"
    _ "github.com/go-sql-driver/mysql"
    "database/sql"
)

type WebMux struct{
}

func (p *WebMux) ServeHTTP(w http.ResponseWriter,r *http.Request){
    switch r.URL.Path{
        case "/":
            sayHello(w,r)
            return
        case "/login":
            login(w,r)
            return
        default:
            http.NotFound(w,r)
            return
    }
}

func checkErr(err error) {
    if err != nil {
        panic(err)
    }
}

func sayHello(w http.ResponseWriter,r *http.Request){
    r.ParseForm()
    fmt.Println(r.Form)
    fmt.Println("path:",r.URL.Path)
    fmt.Println("scheme:",r.URL.Scheme)
    fmt.Println(r.Form["url_long"])
    for k,v:=range r.Form{
        fmt.Println("key:",k)
        fmt.Println("val:",strings.Join(v," "))
    }
    fmt.Fprintf(w,"Hello,welcome to Go web world!")
}

func login(w http.ResponseWriter,r *http.Request){
    fmt.Println("method:",r.Method)
    if r.Method=="GET" {
        t,_:=template.ParseFiles("gtpl/login.html")
        t.Execute(w,nil)
    } else {
        r.ParseForm()
        fmt.Println("username:",r.Form["username"][0])
        fmt.Println("password:",r.Form["password"][0])

        //连接数据库
        dbConnStr:="xoops:xoops@tcp(dbserver:3306)/xoops?charset=utf8"
        db,err:=sql.Open("mysql",dbConnStr)
        defer db.Close()
        rows,err:=db.Query("select * from auth_user where password=? and username=?",r.Form["password"][0],r.Form["username"][0])
        checkErr(err)
        if rows.Next() {
            var username,password,usercnname string
            rows.Scan(&username,&password,&usercnname)
            fmt.Fprintf(w,"Hello,%s",usercnname)
        } else {
            fmt.Fprintf(w,"Ooooops!Invalid username or password.")
        }
    }
}
func main(){
    //http.HandleFunc("/",sayHello)
    //err:=http.ListenAndServe(":9090",nil)
    mux:=&WebMux{}
    err:=http.ListenAndServe(":9090",mux)
    if err!=nil {
        log.Fatal("ListenAndServe:",err)
    }
}

login.html页面上使用外联样式表 可是程序执行时不会加载样式。