[Chartjs]-Chart.js plugin annotation line shadow

You could use the following plugin:

https://nagix.github.io/chartjs-plugin-style/

Example code for reference:

var ctx = document.getElementById('canvasId').getContext('2d');
    var myChart = new Chart(ctx, {
        type: 'line',
        data: {
            labels: ["a", "b", "c", "d", "e" ],
            datasets: [{
                data: ["10", "11", "12", "1", "5"],
                shadowOffsetX: 2,
                shadowOffsetY: 4,
                shadowBlur: 5,
                shadowColor: 'rgba(0, 0, 0, 0.5)'
            }]
        },
    });