School/SchoolProject/App.xaml

<Application x:Class="SchoolProject.App"
             xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
             xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
             xmlns:local="clr-namespace:SchoolProject"
             StartupUri="MainWindow.xaml">
    <Application.Resources>
        <Style TargetType="Button">
            <Setter Property="Height" Value="30"></Setter>
            <Setter Property="Width" Value="150"></Setter>
            <Setter Property="BorderBrush" Value="White"></Setter>
            <Setter Property="BorderThickness" Value="2"></Setter>
            <Setter Property="Background" Value="#FF119D82"></Setter>
            <Setter Property="Foreground" Value="White"></Setter>
        </Style>

        <Style x:Key="MainWindow" TargetType="Window">
            <Setter Property="MinHeight" Value="480"></Setter>
            <Setter Property="MinWidth" Value="600"></Setter>
            <Setter Property="FontFamily" Value="Georgia"></Setter>
            <Setter Property="Background" Value="#FF3D92DD"></Setter>
        </Style>

        <Style x:Key="MainPage" TargetType="Page">
            <Setter Property="FontFamily" Value="Georgia"></Setter>
            <Setter Property="Background" Value="#FF3D92DD"></Setter>
        </Style>
        <Style TargetType="DataGrid">
            <Setter Property="CanUserAddRows" Value="False"></Setter>
            <Setter Property="CanUserDeleteRows" Value="False"></Setter>
            <Setter Property="AutoGenerateColumns" Value="False"></Setter>
            <Setter Property="Background" Value="Transparent"></Setter>
            <Setter Property="ColumnWidth" Value="*"></Setter>
            <Setter Property="IsReadOnly" Value="True"></Setter>
            <Setter Property="BorderBrush" Value="#FF119D82"></Setter>
        </Style>

        <Style TargetType="TextBox">
            <Setter Property="Height" Value="20"></Setter>
            <Setter Property="Background" Value="Transparent"></Setter>
            <Setter Property="BorderBrush" Value="White"></Setter>
            <Setter Property="BorderThickness" Value="0,0,0,2"></Setter>
        </Style>

        <Style TargetType="DatePickerTextBox">
            <Setter Property="Height" Value="25"></Setter>
            <Setter Property="Background" Value="Transparent"></Setter>
            <Setter Property="BorderBrush" Value="White"></Setter>
            <Setter Property="BorderThickness" Value="0,0,0,2"></Setter>
        </Style>

        <Style TargetType="DatePicker">
            <Setter Property="BorderBrush" Value="White"></Setter>
        </Style>
        
        <Style TargetType="DataGridColumnHeader">
            <Setter Property="Background" Value="#FF119D82"></Setter>
            <Setter Property="Foreground" Value="White"></Setter>
        </Style>
    </Application.Resources>
</Application>