3. Шаблон админки

Вынесем все из секции content в отдельный слой resources/views/admin/layouts/layout.blade.php

В resources/views/admin/index.blade.php оставим только:

@extends('admin.layouts.layout')

@section('content')
    <!-- Content Header (Page header) -->
    <section class="content-header">
        <div class="container-fluid">
            <div class="row mb-2">
                <div class="col-sm-6">
                    <h1>Главная</h1>
                </div>
                <div class="col-sm-6">
                    <ol class="breadcrumb float-sm-right">
                        <li class="breadcrumb-item"><a href="#">Home</a></li>
                        <li class="breadcrumb-item active">Blank Page</li>
                    </ol>
                </div>
            </div>
        </div><!-- /.container-fluid -->
    </section>

    <!-- Main content -->
    <section class="content">

        <!-- Default box -->
        <div class="card">
            <div class="card-header">
                <h3 class="card-title">Title</h3>

                <div class="card-tools">
                    <button type="button" class="btn btn-tool" data-card-widget="collapse" data-toggle="tooltip"
                            title="Collapse">
                        <i class="fas fa-minus"></i></button>
                    <button type="button" class="btn btn-tool" data-card-widget="remove" data-toggle="tooltip"
                            title="Remove">
                        <i class="fas fa-times"></i></button>
                </div>
            </div>
            <div class="card-body">
                Start creating your amazing application!
            </div>
            <!-- /.card-body -->
            <div class="card-footer">
                Footer
            </div>
            <!-- /.card-footer-->
        </div>
        <!-- /.card -->

    </section>
    <!-- /.content -->
@endsection

@extends('admin.layouts.layout');

@section('content')
    <!-- Default box -->
    <div class="card">
        <div class="card-header">
            <h3 class="card-title">Главная</h3>

            <div class="card-tools">
                <button type="button" class="btn btn-tool" data-card-widget="collapse" data-toggle="tooltip" title="Collapse">
                    <i class="fas fa-minus"></i></button>
                <button type="button" class="btn btn-tool" data-card-widget="remove" data-toggle="tooltip" title="Remove">
                    <i class="fas fa-times"></i></button>
            </div>
        </div>
        <div class="card-body">
            Start creating your amazing application!
        </div>
        <!-- /.card-body -->
        <div class="card-footer">
            Footer
        </div>
        <!-- /.card-footer-->
    </div>
    <!-- /.card -->
@endsection

И вставим секцию в resources/views/admin/layouts/layout.blade.php:

 <!-- Content Wrapper. Contains page content -->
<div class="content-wrapper">
@yield('content')
</div>
<!-- /.content-wrapper -->